OLD IDEAS AND NEW APPLIED TO BOILER CONSTRUCTION.The lower figure shows RobertTrevithick'sfamous boiler, used in operating his locomotive about the year 1804. The original is preserved in the South Kensington Museum, London. The upper figure shows a modern tubular boiler, by way of contrast.
The lower figure shows RobertTrevithick'sfamous boiler, used in operating his locomotive about the year 1804. The original is preserved in the South Kensington Museum, London. The upper figure shows a modern tubular boiler, by way of contrast.
The lower figure shows RobertTrevithick'sfamous boiler, used in operating his locomotive about the year 1804. The original is preserved in the South Kensington Museum, London. The upper figure shows a modern tubular boiler, by way of contrast.
It will be understood from what has been said before, that with all accessions of heat, the expansive power of the vapor is increased,—its molecules becoming increasingly active; hence one of the very obvious advantages of super-heated steam for the purpose of pushing a piston. There are other advantages, however, which are not at first sight so apparent, having to do with the properties of condensation. To understand these, we must pay heed for a few moments to the changes that take place in steam itself in the course of its passage through the cylinder, where it performs its work upon the piston.
Many of these changes were not fully understood by the earlier experimenters, including Watt. Indeed the theory of the steam engine, or rather the general theory of the heat engine, was not worked out until the year 1824, when the Frenchman Carnot took the subject in hand, and performed a series of classical experiments, which led to a nearly complete theoretical exposition of the subject. It remained, however, for the students of thermo-dynamics, about the middle of the nineteenth century, with Clausius and Rankine at their head, to perfect the theory of the steam engine, and the general subject of the mutual relations of heat and mechanical work.
We are not here concerned with any elaboration of details, but merely with a few of the essential principles which enter practically into the operation of the steamengine. It appears, then, that when steam enters the cylinder and begins to thrust back the piston of the steam engine, a portion of the steam is immediately condensed on the walls of the cylinder, owing to the fact that previous condensation of steam has cooled these walls to a certain extent. We have already pointed out that Watt endeavored in his earlier experiments to overcome this difficulty, by equalizing the temperature of the cylinder walls to the greatest practicable extent.
Notwithstanding his efforts, however, and those of numberless later experimenters, it still remains true that under ordinary conditions, particularly if steam enters the cylinder at the saturation point, a very considerable condensation occurs. Indeed this may amount to from thirty to fifty per cent. of the entire bulk of water contained in the quantity of steam that enters the cylinder. This condensation obviously militates against the expansive or working power of the steam. But now as the steam expands, pushing forward the cylinder, it becomes correspondingly rarefied, and immediately a portion of the condensed steam becomes again vaporized, and in so doing it takes up a certain amount of heat and renders it latent. This disadvantageous cycle of molecular transformations is very much modified in the case of super-heated steam, for the obvious reason that such steam may be very much below the saturation point, and hence requires a very much greater lowering of temperature in order to produce condensation of any portion of its mass. Without elaborating details, it suffices to note that in all highly efficient modern engines, steam is employed at a relativelyhigh pressure, and that sometimes this pressure becomes enormous.
As to the compound engine, that also, as has been pointed out, was invented by a contemporary of Watt, Jonathan Hornblower by name, whose patent bears date of 1781. In Hornblower's engine, steam was first admitted to a small cylinder, and then, after performing its work on the piston, was allowed to escape, not into a condensing receptacle, but into a larger cylinder where it performed further work upon another piston. This was obviously an instance of the use of steam expansively, and it has been pointed out that, in consequence, Hornblower was the first to make use of this idea in practise, although it is said that Watt's experiments had even at that time covered this field. The application of the idea to the movement of the second cylinder, however, appears to have been original with Hornblower. Certainly it owed nothing to Watt, who refused to accept the idea, and continued throughout his life to frown upon the compound engine.
Nevertheless, the device had great utility, as subsequent experiments were very fully to demonstrate. The compound engine was revived by Woolf in 1804, and his name rather than Hornblower's is commonly associated with it. The latter experimenter demonstrated that the compound engine has two important merits as against the simple engine. One of these is that the sum of the two forces exerted by the joint action results in a more even and continuous pressurethroughout the cycle than could be accomplished by the action of a single cylinder.
To understand this it must be recalled that when using the expansive property of steam, the piston thrust could not possibly be uniform, since the greatest pressure exerted by the steam would be exerted at the moment before it was shut off from the boiler, and its pressure must then decrease progressively, as it exerts more and more work upon the piston and becomes more expanded, thus obviously retaining less elastic energy. The operation of the fly-wheel largely compensates this difference of pressure in practise, but it would be obviously advantageous could the pressure be equalized; and, as just stated, the compound engine tends to produce this result.
The second, and perhaps the more important merit of the compound engine is, that it is found in practise to keep the cylinders at a more uniform temperature. A moment's reflection makes it clear why this should be the case, since in a single-cylinder engine the exhaust connects with the cool condenser, whereas in the compound engine the exhaust from the first cylinder connects with the second cylinder at only slightly lower temperature.
In many modern engines a third cylinder and sometimes even a fourth is added, constituting what are called respectively triple-expansion and quadruple-expansion engines. The triple-expansion system is very generally employed, especially where it is peculiarly desirable to economize fuel, as, for example, in the case of ships.
COMPOUND ENGINES.COMPOUND ENGINES.
COMPOUND ENGINES.
COMPOUND ENGINES.
COMPOUND ENGINES.
COMPOUND ENGINES.The lower figure illustrates the use of a modern compound engine, directly operating the propeller shaft of a steamship. The middle figure shows a similarly direct application of power to the axes of paddle wheels. The upper figure shows the application of power through a walking beam similar in principle to that of the original Newcomen and Watt engines.
The lower figure illustrates the use of a modern compound engine, directly operating the propeller shaft of a steamship. The middle figure shows a similarly direct application of power to the axes of paddle wheels. The upper figure shows the application of power through a walking beam similar in principle to that of the original Newcomen and Watt engines.
The lower figure illustrates the use of a modern compound engine, directly operating the propeller shaft of a steamship. The middle figure shows a similarly direct application of power to the axes of paddle wheels. The upper figure shows the application of power through a walking beam similar in principle to that of the original Newcomen and Watt engines.
All these improvements, it will be observed, have to do with details that do not greatly modify the steam engine from the original type. The cylinder with its closely fitting piston, as introduced in the Newcomen engine, is retained and constitutes the essential mechanism through which the energy of steam is transferred into mechanical energy. But from a comparatively remote period the idea has prevailed that it might be possible to utilize a different principle; that, in short, if the steam instead of being made to press against a piston were allowed to rush against fan-like blades, adjusted to an axle, it might cause blades and axle to revolve, precisely as a windmill is made to revolve by the pressure of the wind, or the turbine wheel by the pressure of water.
In a word, it has been believed that a turbine engine might be constructed, which would utilize the energy of the steam as advantageously as it is utilized in the piston engine, and at the same time would communicate its power as a direct rotation, instead of as a straight thrust that must be translated into a rotary motion by means of a crank or other mechanism.
In point of fact, James Watt himself invented such an engine, and patented it in 1782, though there is no evidence that he ever constructed even a working model. His patent specifications show "a piston in the form of a closely-fitting radial arm, projecting from an axial shaft in a cylinder. An abutment, arranged as a flap is hinged near a recess in the side of the cylinder, andswings while remaining in contact with the piston. Steam is admitted to the chamber on one side of the flap, and so causes an unbalanced pressure upon the radial arm."
This arrangement has been re-invented several times. Essentially the same principle is utilized by Joshua Routledge, whose name is well known in connection with the engineer's slide-rule. A model of this engine is preserved in the South Kensington Museum, and the apparatus is described in the catalogue of the Museum as follows:
"The piston revolves on a shaft passing through the centre of the cylinder casing. The flap or valve hinged to the casing, with its free end resting upon the piston, acts like the bottom of an ordinary engine cylinder. The steam inlet port is on one side of the hinge, and the exhaust port on the other. The admission of steam is controlled by a side valve, actuated by an eccentric on the fly-wheel shaft, so that the engine could work expansively, and the steam pressure resisting the lifting of the flap would also be greatly reduced, so diminishing the knock at this point, which, however, would always be a serious cause of trouble. The exhaust steam passes down to a jet condenser, provided with a supply of water from a containing tank, from which the injection is admitted through a regulating valve. The air pump, which draws the air and water from the condenser and discharges them through a pipe passing out at the end of the tank, is a rotary machine constructed like the engine and driven by spur gearing from the fly-wheel shaft. Some efforts have been made to prevent leakageby forming grooves in the sides of the revolving piston and filling them with soft packing."
Sundry other rotary engines, some of them actual working models, are to be seen at the South Kensington Museum. There is, for example, one invented by the Rev. Patrick Bell, a gentleman otherwise known to fame as one of the earliest inventors of a practical reaping machine. In this apparatus, "A metal disc is secured to a horizontal axis carried in bearings, and the lower half of the disc is enclosed by a chamber of circular section having its axis a semi-circle. One end of this chamber is closed and provided with a pipe through which steam enters, the exhaust taking place through the open end. The disc is provided with three holes, each fitted with a circular plate turning on an axis radial to the disc, and these plates when set at right angles to the disc become pistons in the lower enclosing chamber. Toothed gearing is arranged to rotate these pistons into the plane of the disc on leaving the cylinder and back again immediately after entering, locking levers retaining them in position during the intervals. The steam pressure upon these pistons forces the disc round, but the engine is non-expansive, and although some provision for packing has been made, the leakage must have been considerable and the wear and tear excessive."
It is stated that almost the same arrangement was proposed by Lord Armstrong in 1838 as a water motor, and that a model subsequently constructed gave over five horse-power at thirty revolutions per minute, with an efficiency of ninety-five per cent.
Another working model of a rotary engine shown at the Museum is one loaned by Messrs. Fielding and Platt in 1888. "The action of this engine depends upon the oscillating motion which the cross of a universal joint has relative to the containing jaws when the system is rotated.
"Two shafts are set at an angle of 165 deg. to each other and connected by a Hooke's joint; one serves as a pivot, the power being taken from the other. Four curved pistons are arranged on the cross-piece, two pointing towards one shaft and two towards the other, and on each shaft or jaw are formed two curved steam cylinders in which the curved pistons work. The steam enters and leaves the base of each cylinder through ports in the shaft, which forms a cylindrical valve working in the bearing as a seating.
"On the revolution of the shafts the pistons reciprocate in their cylinders in much the same way as in an ordinary engine, and the valve arrangement is such that while each piston is receding from its cylinder the steam pressure isdrivingit, and during the in-stroke of each, its cylinder is in communication with the exhaust. There are thus four single-acting cylinders making each a double stroke for one revolution of the driving-shaft. The engine has no dead centres, and has been at 1,000 revolutions per minute."
ROTARY ENGINES.ROTARY ENGINES.The three types of rotary engines here shown are similar in principle, and none of them is of great practical value, though the upper figure shows an engine that has met with a certain measure of commercial success.
ROTARY ENGINES.The three types of rotary engines here shown are similar in principle, and none of them is of great practical value, though the upper figure shows an engine that has met with a certain measure of commercial success.
ROTARY ENGINES.
The three types of rotary engines here shown are similar in principle, and none of them is of great practical value, though the upper figure shows an engine that has met with a certain measure of commercial success.
It is not necessary to describe other of the rotary engines that have been made along more or less similar lines by numerous inventors, models of which are for the most part, as in the case of those just described, to be seen more commonly in museums than in practicalworkshops. Reference may be made, however, to a rotary engine which was invented by a Mr. Hoffman, of Buffalo, New York, about the beginning of the twentieth century, an example of which was put into actual operation in running the machinery of a shop in Buffalo, in 1905.
This engine consists of a solid elliptical shaft of steel, fastened to an axle at one side of its centre, which axis is also the shaft of the cylinder, which revolves about the central ellipse in such a way that at one part of the revolution the cylinder surface fits tightly against the ellipse, while the opposite side of the cylinder supplies a free chamber between the ellipse and the cylinder walls. Running the length of the cylinder are two curved pieces of steel, like longitudinal sections of a tube. These flanges are adjusted at opposite sides of the cylinder and so arranged that their sides at all times press against the ellipse, alternately retreating into the substance of the cylinder, and coming out into the free chamber. Steam is admitted to the free chamber through one end of the shaft of ellipse and cylinder and exhausted through the other end. The pressure of the steam against first one end and then the other of the flanges supplies the motive power. This pressure acts always in one direction, and the entire apparatus revolves, the cylinder, however, revolving more rapidly than the central ellipse.
For this engine the extravagant claim is made that there is no limit to its speed of revolution, within the limit of resistance of steel to centrifugal force. It has been estimated that a locomotive might be made to run two hundred or three hundred miles an hour withoutdifficulty, with the Hoffman engine. Such estimates, however, are theoretical, and it remains to be seen what the engine can do in practise when applied to a variety of tasks, and what are its limitations. Certainly the apparatus is at once ingenious and simple in principle, and there is no obvious theoretical reason why it should not have an important future.
Whatever the future may hold, however, it remains true that the first practical solution of the problem of securing direct rotary motion from the action of steam, on a really commercial scale, was solved with an apparatus very different from any of those just described, the inventor being an Englishman, Mr. C. A. Parsons, and the apparatus the steam turbine, the first model of which he constructed in 1884, and which began to attract general attention in the course of the ensuing decade. Public interest was fully aroused in 1897, when Mr. Parson's boat, theTurbinia, equipped with engines of this type, showed a trial speed of 32-3/4 knots per hour, a speed never hitherto attained by any other species of water craft. More recently, a torpedo boat, theViper, equipped with engines developing about ten thousand horse-power, attained a speed of 35-1/2 knots. The success of these small boats led to the equipment of large vessels with the turbine, and on April first, 1905, the first transatlantic liner propelled by this form of engine steamed into the harbor of Halifax, Nova Scotia.
This first ocean liner equipped with the turbine engine is called theVictorian. She is a ship five hundred and forty feet long and sixty feet wide, carrying fifteen hundred passengers. TheVictorianhad shown a speed of 19-1/2 knots an hour on her trial trip, and it had been hoped that she would break the transatlantic record. On her first trip, however, she encountered adverse winds and seas, and did not attain great speed. Her performance was, however, considered entirely satisfactory and creditable.
In the ensuing half-decade several large ships were equipped with engines of the same type, the most famous of these being the Cunard liners,Carmania,Lusitania, andMauretania. The two last-named ships are sister craft, and they are the largest boats of any kind hitherto constructed. TheLusitaniawas first launched and she entered immediately upon a record-breaking career, only to be surpassed within a few months by theMauretania, which soon acquired all records for speed and endurance.
Fuller details as to the performance of these vessels will be found in another place. Here we are of course concerned with the Parsons turbine engine itself rather than with its applications.
This turbine engine constitutes the first really important departure from the old-type steam engine, thus realizing the dream of the seventeenth-century Italian, Branca, to which reference was made above. Mr. Parsons' elaboration of the idea developed a good deal of complexity as regards the number of parts involved, yet his engine is of the utmost simplicity in principle.It consists of a large number of series of small blades, each series arranged about a drum which revolves. Between the rings of revolving blades are adjusted corresponding rings of fixed blades, which project from the casing to the cylinder, and by means of which the steam is regulated in direction, so that it strikes at the proper angle against the revolving blades of the turbine.
In practise, three series of cylindrical drums are used, each containing a large number of rings of blades of uniform size; but each successive drum having longer blades, to accommodate the greater volume of the expanding steam. The steam is fed against the first series of blades in gusts, which may be varied in frequency and length to meet the requirements of speed. After impinging on the first circle of blades, the steam passes to the next under slightly reduced pressure, and the pressure is thus successively stepped down from one set of blades to another until it is ultimately reduced from say two hundred pounds to the square inch, to one pound to the square inch before it passes to the condenser and ceases to act.
There is thus a fuller utilization of the kinetic energy of the gas, through carrying it from high to low pressure, than is possible with the old type of cylinder-and-piston engine. On the other hand, there is a constant loss due to the fact that the blades of the turbine can not fit with absolute tightness against the cylinder walls. The net result is that the compound turbine, as at present developed, appears to have about the same efficiency as the best engine of the old type.
One capital advantage of the turbine is that it keepsthe cylinder walls at a more uniform temperature than is possible even with a compound engine of the old type. Another advantage is that the power of the turbine is applied directly to cause rotation of the shaft, whereas no satisfactory means has ever been discovered hitherto of making the action of the steam engine rotary, except with the somewhat disadvantageous crank-shaft. This fact of adjustment of the turbine blades to the revolving shaft seems to make this form of engine particularly adapted to use in steamships. It is also highly adapted to revolving the shaft of a dynamo, and has been largely applied to this use. Needless to say, however, it may be applied to any other form of machinery. It would be difficult at the present stage of its development to predict the extent to which the turbine will ultimately supersede the old type of engine. Its progress has already been extraordinary, however, as an engineer pointed out in the LondonTimesof August 14, 1907, in the following words:
"When the steam turbine was introduced by Mr. Parsons some 25 years ago, in the form of a little model, which is now in the South Kensington Museum, and the rotor of which may easily be held stationary by the hand against the full blast of the steam, who would have been rash enough to predict, except perhaps the far-seeing inventor himself, that a vessel 760 feet long, loaded to 37,000 tons displacement, drawing 32 ft. 9 in. of water, and providing accommodation for 2,500 people, could be propelled at a speed of 24.5 knots per hour, which it is hoped she may maintain over the 3,000 miles of the Atlantic voyage?
"From this small model, which will in time become as historic as theRocketof Stephenson, and which is only some few inches in diameter, the turbine has been developed gradually in size. The cylindrical casings which take the place of the complicated machinery of the piston engine in the engine room of theLusitaniacontain drums, which in the high-pressure turbines are 8 feet in diameter and in the low-pressure 11 ft. 8 in., and from which thousands of curved blades project, the longest of which are 22 inches, and against which the steam impinges in its course from the boiler to the condenser.
"Not only has the steam turbine justified the confidence of those who have labored so successfully in its development, but no other great invention has proceeded from the laboratory stage to such an important position in the engineering world in such a short space of time. This would not have happened if some inherent drawback, such as lack of economy in steam consumption, existed, and as the turbine has been proved to be, for land purposes, very economical, there seems to be no reason to doubt that marine turbines, working as they do at full load almost continually, will show likewise that the coal bill is not increased, but perhaps diminished by their use.
"The records of the vibrations of the hull which were taken during the trials by Schlick's instruments showed that the vertical vibration was 60 per minute on the run, which was due to the propellers, and which may be further modified. The horizontal vibration was almost unnoticeable, while the behavior of theship in the heavy seas she encountered in her long-distance runs was good, the roll from side to side having a period of 18 seconds. The great length of this ship and the gyrostatic action of the heavy rotating masses of the machinery ought to render her almost insensible to the heaviest Atlantic rollers; certainly as far as pitching is concerned."
THE ORIGINAL PARSON'S TURBINE ENGINE AND THE RECORD-BREAKING SHIP FOR WHICH IT IS RESPONSIBLE.THE ORIGINAL PARSON'S TURBINE ENGINE AND THE RECORD-BREAKING SHIP FOR WHICH IT IS RESPONSIBLE.This small turbine engine, with which Mr. Parson's early experiments were made in 1884, is preserved in the South Kensington Museum, London. At the time when it was made it seemed scarcely more than a toy, and engineers in general doubted that the principle it employed could ever be made commercially available. Yet within the lifetime of its inventor engines built on this model have come to be the most powerful of force transmuters. The "Mauretania," the largest, and thanks to her turbine engines the speediest, of ships, is here presented on the same page with the little original turbine model, as illustrating vividly the practical development of a seemingly visionary idea.
THE ORIGINAL PARSON'S TURBINE ENGINE AND THE RECORD-BREAKING SHIP FOR WHICH IT IS RESPONSIBLE.This small turbine engine, with which Mr. Parson's early experiments were made in 1884, is preserved in the South Kensington Museum, London. At the time when it was made it seemed scarcely more than a toy, and engineers in general doubted that the principle it employed could ever be made commercially available. Yet within the lifetime of its inventor engines built on this model have come to be the most powerful of force transmuters. The "Mauretania," the largest, and thanks to her turbine engines the speediest, of ships, is here presented on the same page with the little original turbine model, as illustrating vividly the practical development of a seemingly visionary idea.
THE ORIGINAL PARSON'S TURBINE ENGINE AND THE RECORD-BREAKING SHIP FOR WHICH IT IS RESPONSIBLE.
This small turbine engine, with which Mr. Parson's early experiments were made in 1884, is preserved in the South Kensington Museum, London. At the time when it was made it seemed scarcely more than a toy, and engineers in general doubted that the principle it employed could ever be made commercially available. Yet within the lifetime of its inventor engines built on this model have come to be the most powerful of force transmuters. The "Mauretania," the largest, and thanks to her turbine engines the speediest, of ships, is here presented on the same page with the little original turbine model, as illustrating vividly the practical development of a seemingly visionary idea.
A more general comment upon the turbine engine, with particular reference to its use in America, is made by Mr. Edward H. Sanborn in an article onMotive Power Appliances, in the Twelfth Census Report of the United States, Vol. X. part IV.
"Apart from its demonstrated economy," says Mr. Sanborn, "other important advantages are claimed for the steam turbine, some of which are worthy of brief mention.
"There is an obvious advantage in economy of space as compared with the reciprocating engine. The largest steam turbine constructed in the United States is one of 3,000 horse-power, which is installed in the power house of the Hartford Electric Light Company, Hartford, Conn. The total weight of this motor is 28,000 pounds, its length over all is 19 feet 8 inches, and its greatest diameter six feet. With the generator to which it is directly connected, it occupies a floor space of 33 feet 3 inches long by 8 feet 9 inches wide.
"Friction is reduced to a minimum in the steam turbine, owing to the absence of sliding parts and the small number of bearings. The absence of internal lubrication is also an important consideration, especially when it is desired to use condensers.
"As there are no reciprocating parts in a steam turbine, and as a perfect balance of its rotating parts is absolutely essential to its successful operation, vibration is reduced to such a small element that the simplest foundations will suffice, and it is safe to locate steam turbines on upper floors of a factory if this be desirable or necessary.
"The perfect balance of the moving parts and the extreme simplicity of construction tend to minimize the wear and increase the life of a turbine, and at the same time to reduce the chance of interruption in its operation through derangement of, or damage to, any of its essential parts.
"Although hardly beyond the stage of its first advent in the motive-power field, the steam turbine has met with much favor, and there is promise of its wide use for the purposes to which it is particularly adapted. At present, however, its uses are restricted to service that is continuous and regular, its particular adaptability being for the driving of electrical generators, pumps, ventilating fans, and similar work, especially where starting under load is not essential.
"Steam turbines are now being built in the United States in all sizes up to 3,000 horse-power. Their use abroad covers a longer period and has become more general. The largest turbines thus far attempted are those of the Metropolitan District Electric Traction Company, of London, embracing four units of 10,000 horse-power each. Several turbines of large size have been operated successfully in Germany."
It should be added that the compound turbine wheelof Parsons is not the only turbine wheel that has proved commercially valuable. There is a turbine consisting of a single ring of revolving blades, the invention of Dr. Gustav De Laval, which has proved itself capable of competing with the old type of engine. To make this form of single turbine operate satisfactorily, it is necessary to have steam under high pressure, and to generate a very high speed of revolution. In practice, the De Laval machines sometimes attain a speed of thirty thousand revolutions per minute. This is a much higher rate of speed than can advantageously be utilized directly in ordinary machinery, and consequently the shaft of this machine is geared to another shaft in such a way as to cause the second shaft to revolve much more slowly.
Justat the time when the type of piston-and-cylinder engine has thus been challenged, it has chanced that a new motive power has been applied to the old type of engine, through the medium of heated gas. The idea of such utilization of a gas other than water vapor is by no means new, but there have been practical difficulties in the way of the construction of a commercial engine to make use of the expansive power of ordinary gases.
The principle involved is based on the familiar fact that a gas expands on being heated and contracts when cool. Theoretically, then, all that is necessary is to heat a portion of air confined in a cylinder, to secure the advantage of its expansion, precisely as the expansion of steam is utilized, by thrusting forward a piston. Such an apparatus constitutes a so-called "caloric" or hot-air engine. As long ago as the year 1807 Sir G. Cayley in England produced a motor of this type, in which the heated air passed directly from the furnace to the cylinder, where it did work while expanding until its pressure was not greater than that of the atmosphere, when it was discharged. The chief mechanical difficulty encountered resulted from the necessity for the employment of very high temperatures; and for a longtime the engine had no great commercial utility. The idea was revived, however, about three-quarters of a century later and an engine operated on Cayley's principle was commercially introduced in England by Mr. Buckett. This engine has a cold-air cylinder above the crank-shaft and a large hot-air cylinder below, while the furnace is on one side enclosed in an air-tight chamber. The fuel is supplied as required through a valve and distributing cone arranged above the furnace and provided with an air lock in which the fuel is stored. At about the time when this hot-air engine was introduced, however, gas and oil engines of another and more important type were developed, as we shall see in a moment.
Meantime, an interesting effort to utilize the expansive property of heated air was made by Dr. Stirling in 1826; his engine being one in which heat was distributed by means of a displacer which moved the mass of air to and fro between the hot and cold portions of the apparatus. He also compressed the air before heating it, thus making a distinct advance in the economy and compactness of the engine. From an engineering standpoint his design has further interest in that it was a practical attempt to construct an engine working on the principle of the theoretically perfect heat engine, in which the cycle of operations is closed, the same mass of air being used throughout. In the theoretically perfect heat engine, it may be added, the cycle of operations may be reversed, there being no loss of energy involved; but in practice, of course, an engine cannot be constructed to meet this ideal condition, as there is necessarilysome loss through dissipation of heat. Dr. Stirling's practical engine had its uses, but could not compete with the steam engine in the general field of mechanical operations to which that apparatus is applied.
Another important practical experimenter in the construction of hot-air engines was John Ericsson, who in 1824 constructed an engine somewhat resembling the early one of Cayley, and in 1852 built caloric engines on such a scale as to be adapted to the propulsion of ships. Notwithstanding the genius of Ericsson, however, engines of this type did not prove commercially successful on a large scale, and in subsequent decades the hot-air motors constructed for practical purposes seldom exceeded one horse-power. Such small engines as these are comparatively efficient and absolutely safe, and they are thoroughly adapted for such domestic purposes as light pumping.
The great difficulty with all these engines operated with heated air has been, as already suggested, that their efficiency of action is limited by the difficulties incident to applying high temperatures to large masses of the gas. There is, however, no objection to the super-heating of small quantities of gas, and it was early suggested that this might be accomplished by exploding a gaseous mixture within a cylinder. It was observed by the experimenters of the seventeenth century that an ordinary gun constitutes virtually an internal-combustion engine; and such experimenters as the Dutchman Huyghens, and the Frenchmen Hautefeuille and Papin, attempted to make practical use of the power setfree by the explosion of gunpowder, their experiments being conducted about the years 1678 to 1689. Their results, however, were not such as to give them other than an historical interest. About a century later, in 1794, the Englishman Robert Street suggested the use of inflammable gases as explosives, and ever since that time there have been occasional experimenters along that line. In 1823 Samuel Brown introduced a vacuum gas engine for raising water by atmospheric pressure. The first fairly practical gas engine, however, was that introduced by J. J. E. Lenoir, who in 1850 proposed an engine working with a cycle resembling that of a steam engine. His engine patented in 1860 proved to be a fairly successful apparatus. This engine of Lenoir prepared the way for gas engines that have since become so enormously important. Its method of action is this:
"To start the engine, the fly-wheel is pulled round, thus moving the piston, which draws into the cylinder a mixture of gas and air through about half its stroke; the mixture is then exploded by an electric spark, and propels the piston to the end of its stroke, the pressure meanwhile falling, by cooling and expansion, to that of the atmosphere when exhaust takes place. In the return stroke the process is repeated, the action of the engine resembling that of the double-acting steam engine, and having a one-stroke cycle. The cylinder and covers are cooled by circulating water. The firing electricity was supplied by two Bunsen batteries and an induction coil, the circuit being completed at the right intervals by contact pieces on an insulating disc on thecrank-shaft; the ignition spark leaped across the space between two wires carried about one-sixth of an inch apart in a porcelain holder."
In 1865 Mons. P. Hugon patented an engine similar to that of Lenoir, except that ignition was accomplished by an external flame instead of by electricity. The ignition flame was carried to and fro in a cavity inside a slide valve, moved by a cam so as to get a rapid cut-off, and permanent lights were maintained at the ends of the valve to re-light the flame-ports after each explosion. The gas was supplied to the cylinder by rubber bellows, worked by an eccentric on the crank-shaft. This engine could be operated satisfactorily, except as to cost, but the heavy gas consumption made it uneconomical.
An important improvement in this regard was introduced by the Germans, Herrn. E. Langen and N. A. Otto, who under patents bearing date of 1866 introduced a so-called "free" piston arrangement—that is to say an arrangement by which the piston depends for its action partly upon the momentum of a fly-wheel. This principle had been proposed for a gas engine as early as 1857, but the first machine to demonstrate its feasibility was that of Langen and Otto. Their engine greatly decreased the gas consumption and hence came to be regarded as the first commercially successful gas engine. It was, however, noisy and limited to small sizes. The cycle of operations of an engine of this type is described as follows:
GAS AND OIL ENGINES.GAS AND OIL ENGINES.Lower right-hand figure, a very early type of commercially successful gas engine. It has a "free" piston, an arrangement that was first proposed for a gas engine in 1857, but only brought into practical form by Langen & Otto under their patent of 1866. Upper figure, the gas engine patented by Lenoir in 1860, one of the very first practically successful engines. Lower left-hand figure, a sectional view of a modern gas engine of the type used as the motor of the automobile.
GAS AND OIL ENGINES.Lower right-hand figure, a very early type of commercially successful gas engine. It has a "free" piston, an arrangement that was first proposed for a gas engine in 1857, but only brought into practical form by Langen & Otto under their patent of 1866. Upper figure, the gas engine patented by Lenoir in 1860, one of the very first practically successful engines. Lower left-hand figure, a sectional view of a modern gas engine of the type used as the motor of the automobile.
GAS AND OIL ENGINES.
Lower right-hand figure, a very early type of commercially successful gas engine. It has a "free" piston, an arrangement that was first proposed for a gas engine in 1857, but only brought into practical form by Langen & Otto under their patent of 1866. Upper figure, the gas engine patented by Lenoir in 1860, one of the very first practically successful engines. Lower left-hand figure, a sectional view of a modern gas engine of the type used as the motor of the automobile.
"(a) The piston is lifted about one-tenth of its travel by the momentum of the fly-wheel, thus drawing in a charge of gas and air.
"(b) The charge is ignited by flame carried in by a slide valve.
"(c) Under the impulse of the explosion, the piston shoots upward nearly to the top of the cylinder, the pressure in which falls by expansion to about 4 lbs. absolute, while absorbing the energy of the piston.
"(d) The piston descends by its own weight and the atmospheric pressure, and in doing so causes a roller-clutch on a spur-wheel gearing with a rack on the piston-rod to engage, so that the fly-wheel shaft shall be driven by the piston; during this down-stroke the pressure increases from 4 lbs. absolute to that of the atmosphere, and averages 7 lbs. per square inch effective throughout the stroke.
"(e) When the piston is near the bottom of the cylinder, the pressure rises above atmospheric, and the stroke is completed by the weight of the piston and rack, and the products of combustion are expelled.
"(f) The fly-wheel now continues running freely till its speed, as determined by a centrifugal governor, falls below a certain limit when a trip gear causes the piston to be lifted the short distance required to recommence the cycle.
"Ignition is performed by an external gas jet, near a pocket in the slide valve by which the charge is admitted; this pocket carries flame to the charge, thus igniting it without allowing any escape. The valve also connects the interior of the cylinder with the exhaust pipe, and a valve in the latter controlled by the governor throttles the discharge, and so defers the next stroke until the speed has fallen below normal. To run the engine emptyabout four explosions per minute are necessary, and at full power 30 to 35 are made, so that about 28 explosions per minute are available for useful work under the control of the governor."
The definitive improvement in this gas engine was introduced in 1876 by Dr. N. A. Otto, when he compressed the explosive mixture in the working cylinder before igniting it. This expedient—so all-important in its results—had been suggested by William Barnett in 1838, but at that time gas engines were not sufficiently developed to make use of the idea. Now, however, Dr. Otto demonstrated that by compressing the gas before exploding it a much more diluted mixture can be fired, and that this gives a quieter explosion, and a more sustained pressure during the working stroke, while as the engine runs at a high speed the fly-wheel action is generally sufficient to correct the fluctuations arising from there being but one explosion for four strokes of the piston.
In this perfected engine, then, the method of operation is as follows:
The piston is pulled forward with the application of some outside force, which in practice is supplied by the inertia of the fly-wheel, or in starting the engine by the action of a crank with which every user of an automobile is familiar. In being pulled forward, the piston draws gas into the cylinder; as the piston returns, this gas is compressed; the compressed gas, constituting an explosive mixture, is then ignited by a piece of incandescent metal or by an electric spark; the exploding gas expands, pushing the piston forward, this being theonly thrust during which work is done; the returning piston expels the expanded gas, completing the cycle. Thus there are three ineffective piston thrusts to one effective thrust. Nevertheless, the engine has proved a useful one for many purposes.
This so-called Otto cycle has been adopted in almost all gas and oil engines, the later improvements being in the direction of still higher compression, and in the substitution of lift for slide valves. There has been a steady increase in the size and power of such engines, the large ones usually introducing two or more working cylinders so as to secure uniform driving. Cheap forms of gas have been employed such as those made by decomposing water by incandescent fuel, and it has been proved possible thus to operate gas-power plants on a commercial scale in competition with the most economical steam installations.
A practical modification of vast importance was introduced when it was suggested that a volatile oil be employed to supply the gas for operation in an internal combustion engine. There was no new principle involved in this idea, and the Otto cycle was still employed as before; but the use of the volatile oil—either a petroleum product or alcohol—made possible the compact portable engine with which everyone is nowadays familiar through its use in automobiles and motor boats. The oil commonly used is gasoline which is supplied to the cylinder through a so-called carburettor in which the vapors of gasoline are combined with ordinary air to make an explosive mixture. The introduction of this now familiar type of motor is to a large extent due toHerr G. Daimler, who in 1884 brought out a light and compact high-speed oil engine. About ten years later Messrs. Panhard and Levassor devised the form of motor which has since been generally adopted. Few other forms of mechanisms are better known to the general public than the oil engine with its two, four, six, or even eight cylinders, as used in the modern automobile. As everyone is aware, it furnishes the favorite type of motor, combining extraordinary power with relative lightness, and making it feasible to carry fuel for a long journey in a receptacle of small compass.
With the gas engines a complication arises precisely opposite to that which is met with in the case of the cylinder of the steam engine—the tendency, namely, to overheating of the cylinder. To obviate this it is customary to have the cylinder surrounded by a water jacket, though air cooling is used in certain types of machines. About fifty per cent. of the total heat otherwise available is lost through this unavoidable expedient.
The rapid introduction of the gas engine in recent years suggests that this type of engine may have a most important future. It has even been predicted that within a few years most trans-Atlantic steamers will be equipped with this type of engine, producing their own gas in transit. It is possible, then, that through this medium the old piston-and-cylinder engine may retain its supremacy, as against the turbine. For the moment, at any rate, the gas engine is gaining popularity, not merely in its application to the automobile, but for numerous types of small stationary engines as well.
In this connection it will be interesting to quote the report of the Special Agent of the Twelfth Census of the United States, as showing the status of gas engines and steam engines in the year 1902.
"The decade between 1890 and 1900," he says, "was a period of marked development in the use of gas engines, using that term to denote all forms of internal combustible engines, in which the propelling force is the explosion of gaseous or vaporous fuel in direct contact with a piston within a closed cylinder. This group embraces those engines using ordinary illuminating gas, natural gas, and gas made in special producers installed as a part of the power plant, and also vaporised gasoline or kerosene. This form of power for the first time is an item of consequence in the returns of the present census, and the very large increase in the horse-power in 1900 as compared with 1890 indicates the growing popularity of this class of motive power.
"In 1890 the number of gas engines in use in manufacturing plants was not reported, but their total power amounted to only 8,930 horse-power, or one-tenth of one per cent of the total power utilized in manufacturing operations. In 1900, however, 14,884 gas engines were reported, with a total of 143,850 horse-power, or 1.3 per cent of the total power used for manufacturing purposes. This increase from 8,930 horse-power to 143,850 horse-power, a gain of 134,920 horse-power, is proportionately the largest increase in any form of primary power shown by a comparison of the figures of theEleventh and Twelfth censuses, amounting to 1,510.9 per cent.
"Within the past decade, and more particularly during the past five years, there has been a marked increase in the use of this power in industrial establishments for driving machinery, for generating electricity, and for other kindred uses. At the same time, internal-combustion engines have increased in popularity for uses apart from manufacturing, and the amount of this kind of power in use for all purposes in 1900 was, doubtless, very much larger than indicated by the figures relating to manufacturing plants alone.
"The average horse-power per gas engine in 1900 was 9.7 horse-power. There are no available statistics upon which to base a comparison of this average with the average for 1890, but it is doubtful if there has been any very material change in ten years; for while gas engines are built in much larger sizes than ever before, there has been also a great increase in the number of small engines for various purposes.
"The large increase in the use of internal-combustion engines has been due to the rapid improvements that have been made in them, their increased efficiency and economy, their decreased cost, and the wider range of adaptability that has been made practicable.
"Steam still continues to be preeminently the power of greatest importance, and the census returns indicate that the proportion of steam to the total of all powers has increased very largely in the past thirty years. In 1870 steam furnished 1,215,711 horse-power, or 51.8 per cent of a total of 2,346,142; in 1880 the amount ofsteam power used was 2,185,458 horse-power out of a total of 3,410,837, or 64.1 per cent; in 1890 out of an aggregate of 5,954,655 horse-power, 4,581,595, or 76.9 per cent was steam; while in 1900 steam figured to the extent of 8,742,416 horse-power, or 77.4 per cent, in a total of 11,300,081. This increase in thirty years, from 51.8 per cent to 77.4 per cent of the total power, shows how much more rapidly the use of steam power has increased than other primary sources of power.
"The tendency toward larger units in the use of steam power is shown inadequately by the increase in the average horse-power per engine from 39 horse-power in 1880, to 51 horse-power in 1890, and 56 horse-power in 1900.
"The tendency toward great operations which has been such a conspicuous feature of industrial progress during the past ten years, has shown itself strikingly in the use of units of larger capacity in nearly every form of machinery, and nowhere has this tendency been more marked than in the motive power by which the machinery is driven. At the same time there has been an increase in the use of small units, which tends to destroy the true tendency in steam engineering in these statistics. For example, a steam plant consisting of one or more units of several thousand horse-power may also embrace a number of small engines of only a few horse-power each, the use of which is necessitated by the magnitude of the plant, for the operation of mechanical stokers, the driving of draft fans, coal and ash conveyors, and other work requiring power in small units. On this account the average horse-power of steam engines in use atdifferent census periods fails to afford a true basis for measuring progress toward larger units during the past ten years.
"Developments of the past few years in the distribution of power by the use of electric motors have served to accelerate the tendency toward larger steam units and the elimination of small engines in large plants and to change completely the conditions just described. For example: In one of the largest power plants in the world, which is now being installed, all the stokers, blowers, conveyors, and other auxiliary machinery are to be driven by electric motors. Such rapidly changing conditions tend to invalidate any comparisons of statistical averages deduced from figures for periods even but a few years apart.
"Comparison of two important industries will illustrate the foregoing. The average horse-power of the steam engine used in the cotton mills of the United States in 1890 was 198, and in 1900 it was 300.
"In the iron and steel industry the average horse-power per engine in 1890 was 171, and in 1900 it was 235. In the cotton mills the use of single large units of motive power, with few auxiliary engines of small capacity, gives the largest horse-power per engine of any industry; while in the iron and steel industry the average of the motive power proper, although probably larger than in the manufacture of cotton goods, is reduced by the large number of small engines which are used for auxiliary purposes in every iron and steel plant."
It will be understood that the object of exploding the mixed gases in the oil engine is to produce sudden heatingof the entire gas. There is no reason whatever for introducing the gasoline beyond this. Could a better method of heating air be devised, the oil might be entirely dispensed with, and the safety of the apparatus enhanced, as well as the economy of operation. Efforts have been made for fifty years to construct a hot-air engine that would compete with steam successfully. In the early fifties, as already noted, Ericsson showed the feasibility of substituting hot air for steam, but although he constructed large engines, their power was so slight that he was obliged to give up the idea of competing with steam, and to use his engines for pumping where very small power was required.
The great difficulty was that it was not found practicable to heat the air rapidly. All subsequent experimenters have met with the same difficulty until somewhat recently. It is now claimed, however, that a means has been found of rapidly heating the air, and it is even predicted that the hot-air engine will in due course entirely supersede the steam engine. Mr. G. Emil Hesse, in an article inThe American Inventor, for April 15, 1905, describes a Svea caloric engine as having successfully solved the problem of rapidly heating air. The methods consist in breaking up the air into thin layers and passing it over hot plates, where it rapidly absorbs heat. It passes from the heater to the power cylinder which resembles the cylinder of a steam engine; thence after expanding and doing its work it is exhausted into the atmosphere. Large engines may use the same air over and over again under pressure of one hundred pounds per square inch, alternately heatingand cooling it. A six horse-power engine of this type is said to have a cylinder four and one-half inches in diameter and a stroke of four and seven-eighth inches, and makes four hundred and fifty revolutions per minute. The heater is twenty inches in diameter, sixteen inches long, and has a heating surface of sixty square feet. The total weight of heater and engine complete is four hundred pounds for a half horse-power Ericsson engine.
"The Svea heater," says Mr. Hesse, "absorbs the heat as perfectly as an ordinary steam boiler, and the heat-radiating surface of both heater and engine is not larger than that of a steam plant of the same power, thereby placing the two motors on the same basis, as far as the utilization of the heat in the fuel itself is concerned.
"The advantage which every hot-air engine has over the steam engine is the amount of heat saved in the vaporization of the water. It is now well known that one gas is as efficient as another for the conversion of heat into power. Air and steam at 100° C. are consequently on the same footing and ready to be superheated. The amount of heat required to bring the two gases to this temperature is, however, very different.
"With an initial temperature of 10° C. for both air and water, we find that one kilogram of steam requires 90 + 537 = 627 thermal units, and one kilogram of air 0.24 × 90 = 21.6 thermal units. Some heat is recovered if the feed water is heated and the steam condensed, but the difference is still so great as to altogether exclude steam as a competitor, provided air can be as readily handled.
"Having now the means to rapidly heat the air, the outlook for the external-combustion engine is certainly very promising.
"The saving of more than half the coal now used by the steam engine will be of tremendous importance to the whole world."
To what extent this optimistic prediction will be verified is a problem for the future to decide.
Inour studies of the steam engine and gas engine we have been concerned with workers of infinitesimal size. Yet, if we are to believe the reports of the modern investigator, the molecules of steam or of ignited gas are small only in a relative sense, and there is a legion of workers compared with which the molecules are really gigantic in size. These workers are the atoms, and the yet more minute particles of which, according to the most recent theories, they are themselves composed.
These smallest conceivable particles, the constituents of the atoms, are called electrons. They are a discovery of the physicists of the most recent generation. According to the newest theories they account for most—perhaps for all—of the inter-molecular and inter-atomic forces; they are indeed the ultimate repositories of those stores of energy which are known to be contained in all matter. The theories are not quite as fully developed as could be wished, but it would appear that these minutest particles, the electrons, are the essential constituents of the familiar yet wonderful carrier of energy which we term electricity. In considering the share of electricity in the world's work, therefore, we shall do well at the outset to put ourselves in touch with recentviews as to the nature of this most remarkable of workers.
On every side in this modern world we are confronted by this strange agent, electricity. The word stares us in the face on every printed page. The thing itself is manifest in all departments of our every-day life. You go to your business in an electric car; ascend to your office in an electric elevator; utilize electric call-bells; receive and transmit messages about the world and beneath the sea by electric telegraph. Your doctor treats you with an electric battery. Your dentist employs electric drills and electric furnaces. You ride in electric cabs; eat food cooked on electric stoves; and read with the aid of electric light. In a word, the manifestations of electricity are so obvious on every side that there can be no challenge to the phrasing which has christened this the Age of Electricity.
But what, then, is this strange power that has produced all these multifarious results? It would be hard to propound a scientific query that has been more variously answered. Ever since the first primitive man observed the strange effect produced by rubbing a piece of amber, thoughtful minds must have striven to explain that effect. Ever since the eighteenth-century scientist began his more elaborate studies of electricity, theories in abundance have been propounded. And yet we are not quite sure that even the science of to-day can give a correct answer as to the nature of electricity. At the very least, however, it is able to give some interesting suggestions which seem to show that we are in a fair way to solve this world-old mystery. And, curiouslyenough, the very newest explanations are not so very far away from some eighteenth-century theories which for a long time were looked at askance if not altogether discarded. In particular, the theory of Benjamin Franklin, which considered electricity as an immaterial fluid bearing certain curious relations to tangible matter, is found to serve singularly well as an aid to the interpretation of the very newest experiments.
Such being the case, we must consider this theory of Franklin's somewhat in detail. Perhaps we cannot do better than state the theory in the words of the celebrated physicist, Dr. Thomas Young, as given in his work on natural philosophy, published in 1807. By quoting from this old work we shall make sure that we are not reading any modern interpretations into the theory. "It is supposed," says Young, "that a peculiar ethereal fluid pervades the pores, if not the actual substance of the earth and of all other material bodies, passing through them with more or less facility, according to their different powers of conducting it; that particles of this fluid repel each other, and are attracted by particles of common matter; that particles of common matter also repel each other; and that these attractions and repulsions are equal among themselves, and vary inversely as to squares of the distances of the particles. The effects of this fluid are distinguished from those of all other substances by an attractive or repulsive quality, which it appears to communicate to different bodies,and which differs in general from other attractions and repulsions by its immediate diminution or cessation when the bodies, acting on each other, come into contact, or are touched by other bodies.... In general, a body is said to be electrified when it contains, either as a whole or in any of its parts, more or less of the electric fluid than is natural to it.... In this common neutral state of all bodies, the electrical fluid, which is everywhere present, is so distributed that the various forces hold each other exactly in equilibrium and the separate results are destroyed, unless we choose to consider gravitation itself as arising from a comparatively slight inequality between the electrical attractions and repulsions."
The salient and striking feature of this theory, it will be observed, is that the electrical fluid, under normal conditions, is supposed to be incorporated everywhere with the substance of every material in the world. It will be observed that nothing whatever is postulated as to the nature or properties of this fluid beyond the fact that its particles repel each other and are attracted by the particles of common matter; it being also postulated that the particles of common matter likewise repel each other under normal conditions.
At the time when Franklin propounded his theory, there was a rival theory before the world, which has continued more or less popular ever since, and which is known as the two-fluid theory of electricity. According to this theory, there are two uncreated and indestructible fluids which produce electrical effects. One fluid may be called positive, the other negative. The particlesof the positive fluid are mutually repellent, as also are the particles of the negative fluid, but, on the other hand, positive particles attract and are attracted by negative particles. We need not further elaborate the details of this two-fluid theory, because the best modern opinion considers it less satisfactory than Franklin's one-fluid theory. Meantime, it will be observed that the two theories have much in common; in particular they agree in the essential feature of postulating an invisible something which is not matter, and which has strange properties of attraction and repulsion.
These properties of attraction and repulsion constituted in the early day the only known manifestations of electricity; and the same properties continue to hold an important place in modern studies of the subject. Electricity is so named simply because amber—the Latinelectrum—was the substance which, in the experience of the ancients, showed most conspicuously the strange property of attracting small bodies after being rubbed. Modern methods of developing electricity are extremely diversified, and most of them are quite unsuggestive of the rubbing of amber; yet nearly all the varied manifestations of electricity are reducible, in the last analysis, to attractions and repulsions among the particles of matter.
As to the alleged immaterial fluids which, according to the theories just mentioned, make up the real substance of electricity, it was perfectly natural that they should be invented by the physicists of the elder day. All the conceptions of the human mind are developed through contact with the material world; and it isextremely difficult to get away, even in theory, from tangible realities. When the rubbed amber acquires the property of drawing the pith ball to it, we naturally assume that some change has taken place in the condition of the amber; and since the visible particles of amber appear to be unchanged—since its color, weight, and friability are unmodified—it seems as if some immaterial quality must have been added to, or taken from it. And it was natural for the eighteenth-century physicist to think of this immaterial something as a fluid, because he was accustomed to think of light, heat, and magnetism as being also immaterial fluids. He did not know, as we now do, that what we call heat is merely the manifestation of varying "modes" of motion among the particles of matter, and that what we call light is not a thingsui generis, but is merely our recognition of waves of certain length in the all-pervading ether. The wave theory of light had, indeed, been propounded here and there by a philosopher, but the theory which regarded light as a corpuscular emanation had the support of no less an authority than Sir Isaac Newton, and he was a bold theorist that dared challenge it. When Franklin propounded his theory of electricity, therefore, his assumption of the immaterial fluid was thoroughly in accord with the physical doctrines of the time.
But about the beginning of the nineteenth century the doctrine of imponderable fluids as applied to light and heat was actively challenged by Young and Fresneland by Count Rumford and Humphry Davy and their followers, and in due course the new doctrines of light and heat were thoroughly established. In the light of the new knowledge, the theory of the electric fluid or fluids seemed, therefore, much less plausible. Whereas the earlier physicists had merely disputed as to whether we must assume the existence of two electrical fluids or of only one, it now began to be questioned whether we need assume the existence of any electrical fluid whatever. The physicists of about the middle of the nineteenth century developed the wonderful doctrine of conservation of energy, according to which one form of force may be transformed into another, but without the possibility of adding to, or subtracting from, the original sum total of energy in the universe. It became evident that electrical force must conform to this law. Finally, Clerk-Maxwell developed his wonderful electromagnetic theory, according to which waves of light are of electrical origin. The work of Maxwell was followed up by the German Hertz, whose experiments produced those electromagnetic waves which, differing in no respect except in their length from the waves of light, have become familiar to everyone through their use in wireless telegraphy. All these experiments showed a close relation between electrical phenomena, and the phenomena of light and of radiant heat, and a long step seemed to be taken toward the explanation of the nature of electricity.
The new studies associated electricity with the ether, rather than with the material substance of the electrified body. Many experiments seemed to show that electricityin motion traverses chiefly the surface of the conductor, and it came to be believed that the essential feature of the "current" consists of a condition of strain or stress in the ether surrounding a conductor, rather than of any change in the conductor itself. This idea, which is still considered valid, has the merit of doing away with the thought of action at a distance—the idea that was so repugnant to the mind of Faraday.
So far so good. But what determines the ether strain? There is surelysomethingthat is not matter and is not ether. What is this something? The efforts of many of the most distinguished experimenters have in recent years been directed toward the solution of that question; and these efforts, thanks to the new methods and new discoveries, have met with a considerable measure of success. I must not attempt here to follow out the channels of discovery, but must content myself with stating briefly the results. We shall have occasion to consider some further details as to the methods in a later chapter.
Briefly, then, it is now generally accepted, at least as a working hypothesis, that every atom of matter—be it oxygen, hydrogen, gold, iron, or what not—carries a charge of electricity, which is probably responsible for all the phenomena that the atom manifests. This charge of electricity may be positive or negative, or it may be neutral, by which is meant that the positive and negative charges may just balance. If the positive charge has definite carriers, these are unknown except in association with the atom itself; but the negative charge, on the other hand, is carried by minute particles towhich the name electron (or corpuscle) has been given, each of which is about one thousand times smaller than a hydrogen atom, and each of which carries uniformly a unit charge of negative electricity.
Electrons are combined, in what may be called planetary systems, in the substance of the atom; indeed, it is not certain that the atom consists of anything else but such combinations of electrons, held together by the inscrutable force of positive electricity. Some, at least, of the electrons within the atom are violently active—perhaps whirling in planetary orbits,—and from time to time one or more electrons may escape from the atomic system. In thus escaping an electron takes away its charge of negative electricity, and the previously neutral atom becomes positively electrified. Meanwhile the free electron may hurtle about with its charge of negative electricity, or may combine with some neutral atom and thus give to that neutral atom a negative charge. Under certain conditions myriads of these electrons, escaped thus from their atomic systems, may exist in the free state. For example, the so-calledbeta(ß) rays of radium and its allies consist of such electrons, which are being hurtled off into space with approximately the speed of light. The cathode rays, of which we have heard so much in recent years, also consist of free electrons.
But, for that matter, all currents of electricity whatever, according to this newest theory, consist simply of aggregations of free electrons. According to theory, if the electrons are in uniform motion they produce the phenomena of constant currents of electricity; if theymove non-uniformly they produce electromagnetic phenomena (for example, the waves used in wireless telegraphy); if they move with periodic motion they produce the waves of light. Meanwhile stationary aggregations of electrons produce the so-called electrostatic phenomena. All the various ether waves are thus believed to be produced by changes in the motions of the electrons. A very sudden stoppage, such as is produced when the cathode ray meets an impassable barrier, produces the X-ray.
With these explanations in mind, it will be obvious how closely this newest interpretation of electricity corresponds in its general features with the old one-fluid theory of Franklin. The efforts of the present-day physicist have resulted essentially in an analysis of Franklin's fluid, which gives to this fluid an atomic structure. The new theory takes a step beyond the old in suggesting the idea that the same particles which make up the electric fluid enter also into the composition—perhaps are the sole physical constituents—of every material substance as well. But while the new theory thus extends the bounds of our vision, we must not claim that it fully solves the mystery. We can visualize the ultimate constituent of electricity as an electron one thousand times smaller than the hydrogen atom, which has mass and inertia, and which possesses powers of attraction and repulsion. But as to the actual nature of this ultimate particle we are still in the dark. There are, however, some interesting theories as to its character, which should claim at least incidental attention.
We have all along spoken of the electron as an exceedinglyminute particle, stating indeed, that in actual size it is believed to be about one thousand times smaller than the hydrogen atom, which hitherto had been considered the smallest thing known to science. But we have now to offer a seemingly paradoxical modification of this statement. It is true that inmassor weight the electron is a thousand times smaller than the hydrogen atom, yet at the same time it may be conceived that the limits of space which the electron occupies are indefinitely large. In a word, it is conceived (by Professor J. J. Thomson, who is the chief path-breaker in this field) that the electron is in reality a sort of infinitesimal magnet, having two poles joined by lines or tubes of magnetic force (the so-called Faraday tube), which lines or tubes are of indefinite number and extent; precisely as, on a large scale, our terrestrial globe is such a magnet supplied with such an indefinite magnetic field. That the mass of the electron is so infinitesimally small is explained on the assumption that this mass is due to a certain amount of universal ether which is bound up with the tubes where they are thickest; close to the point in space from which they radiate, which point in space constitutes the focus of the tangible electron.
It will require some close thinking on the part of the reader to gain a clear mental picture of this conception of the electron; but the result is worth the effort. When you can clearly conceive all matter as composed of electrons, each one of which cobwebs space with its system of magnetic tubes, you will at least have a tangible picture in mind of a possible explanation ofthe forces of cohesion and gravitation—in fact, of all the observed cases of seeming action at a distance. If at first blush the conception of space as filled with an interminable meshwork of lines of force seems to involve us in a hopeless mental tangle, it should be recalled that the existence of an infinity of such magnetic lines joining the poles of the earth may be demonstrated at any time by the observation of a compass, yet that these do not in any way interfere with the play of other familiar forces. There is nothing unthinkable, then, in the supposition that there are myriads of minor magnetic centres exerting lesser degrees of force throughout the same space.