TWO APPARATUSES FOR THE UTILIZATION OF ANIMAL POWER.TWO APPARATUSES FOR THE UTILIZATION OF ANIMAL POWER.
TWO APPARATUSES FOR THE UTILIZATION OF ANIMAL POWER.
TWO APPARATUSES FOR THE UTILIZATION OF ANIMAL POWER.
TWO APPARATUSES FOR THE UTILIZATION OF ANIMAL POWER.The upper figure shows the type of portable horse-power machine used for threshing grain in 1851. The lower figure is an inclined-plane horse-gear. The horse stands on the sloping platform tied to the bar in front, so that it is compelled to walk as the platform recedes.
The upper figure shows the type of portable horse-power machine used for threshing grain in 1851. The lower figure is an inclined-plane horse-gear. The horse stands on the sloping platform tied to the bar in front, so that it is compelled to walk as the platform recedes.
The upper figure shows the type of portable horse-power machine used for threshing grain in 1851. The lower figure is an inclined-plane horse-gear. The horse stands on the sloping platform tied to the bar in front, so that it is compelled to walk as the platform recedes.
It is obvious that the amount of work which a horse can accomplish must vary greatly with the size and quality of the horse, and with the particular method by which its energy is applied. For the purposes of comparison, however, an arbitrary amount of work has been fixed upon as constituting what is called a horse-power. This amount is the equivalent of raisingthirty-three thousand pounds of weight to the height of one foot in one minute. It would be hard to say just why this particular standard was fixed upon, since it certainly represents more than the average capacity of a horse. It is, however, a standard which long usage (it was first suggested by Watt, of steam-engine fame) has rendered convenient, and one which the machinist refers to constantly in speaking of the efficiency of the various types of artificial machines. All questions of the exact legitimacy of this particular standard aside, it was highly appropriate that the labor of the horse, which has made up so large a share of the labor of the past, and which is still so extensively utilized, should continue to be taken as the measuring standard of the world's work.
Thestore of energy contained in the atmosphere and in the waters of the globe is inexhaustible. Its amount is beyond all calculation; or if it were vaguely calculated the figures would be quite incomprehensible from their very magnitude. It is not, however, an altogether simple matter to make this energy available for the purposes of useful work. We find that throughout antiquity comparatively little use was made of either wind or water in their application to machinery.
Doubtless the earliest use of air as a motive power was through the application of sails to boats. We know that the Phœnicians used a simple form of sail, and no doubt their example was followed by all the maritime peoples of subsequent periods. But the use of the sail even by the Phœnicians was as a comparatively unimportant accessory to the galaxies of oars, which formed the chief motive power. The elaboration of sails of various types, adequate in extent to propel large ships, and capable of being adjusted so as to take advantage of winds blowing from almost any quarter, was a development of the Middle Ages.
The possibilities of work with the aid of runningwater were also but little understood by the ancients. In the days of slave labor it was scarcely worth while to tax man's ingenuity to invent machines, since so efficient a one was provided by nature. Yet the properties of both air and water were studied by various mechanical philosophers, at the head of whom were Archimedes, whose work has already been referred to, and the famous Alexandrian, Ctesibius, whose investigations became familiar through the publications of his pupil, Hero.
Perhaps the most remarkable device invented by Ctesibius was a fire-engine, consisting of an arrangement of valves constituting a pump, and operating on the principle which is still in vogue. It is known, however, that the Egyptians of a much earlier period used buckets having valves in their bottoms, and these perhaps furnished the foundation for the idea of Ctesibius. It is unnecessary to give details of this fire-engine. It may be noted, however, that the principle of the lever is the one employed in its operation to gain power. A valve consists essentially of any simple hinged substance, arranged so that it may rise or fall, alternately opening and closing an aperture. A mere flap of leather, nailed on one edge, serves as a tolerably effective valve. At least one of the valves used by Ctesibius was a hinged piece of smooth metal. A piston fitted in a cylinder supplies suction when the lever is raised, and pressure when it is compressed, alternately opening the valve and closing the valve through which the water enters the tube. Meantime a second valve alternating with the first permits the water to enter the chambercontaining air, which through its elasticity and pressure equalizes the force of the stream that is ejected from the chamber through the hose.
In the construction of this and various other apparatus, Ctesibius and Hero were led to make careful studies of the phenomena of suction. But in this they were not alone, since numerous of their predecessors had studied the subject, and such an apparatus as the surgeon's cupping glass was familiarly known several centuries before the Christian era. The cupping glass, as perhaps should be explained to the reader of the present day—since the apparatus went out of vogue in ordinary medical practise two or three generations ago—consists of a glass cup in which the air is exhausted, so as to suck blood from any part of the surface of a body to which it is applied. Hero describes a method of exhausting air by which such suction may be facilitated. But neither he nor any other philosopher of his period at all understood the real nature of this suction, notwithstanding their perfect familiarity with numerous of its phenomena. It was known, for example, that when a tube closed at one end is filled with water and inverted with the open end beneath the surface of the water, the water remains in the tube, although one might naturally expect that it would obey the impulses of gravitation and run out, leaving the tube empty. A familiar explanation of this and allied phenomena throughout antiquity was found in thesaying that "Nature abhors a vacuum." This explanation, which of course amounts to no explanation at all, is fairly illustrative of the method of metaphysical word-juggling that served so largely among the earlier philosophers in explanation of the mysteries of physical science.
The real explanation of the phenomena of suction was not arrived at until the revival of learning in the seventeenth century. Then Torricelli, the pupil of Galileo, demonstrated that the word suction, as commonly applied, had no proper application; and that the phenomena hitherto ascribed to it were really due to the pressure of the atmosphere. A vacuum is merely an enclosed space deprived of air, and the "abhorrence" that Nature shows to such a space is due to the fact that air has weight and presses in every direction, and hence tends to invade every space to which it can gain access. It was presently discovered that if the inverted tube in which the water stands was made high enough, the water will no longer fill it, but will sink to a certain level. The height at which it will stand is about thirty feet; above that height a vacuum will be formed, which, for some reason, Nature seems not to abhor. The reason is that the weight of any given column of water about thirty feet in height is just balanced by the weight of a corresponding column of atmosphere. The experiments that gave the proof of this were made by the famous Englishman, Boyle. He showed that if the heavy liquid, mercury, is used in place of water, then the suspended column will be only about thirty inches in height. The weight orpressure of the atmosphere at sea level, as measured by these experiments, is about fifteen pounds to the square inch.
Boyle's further experiments with the air and with other gases developed the fact that the pressure exerted by any given quantity of gas is proportional to the external pressure to which it is subjected, which, after all, is only a special application of the law that action and reaction are equal. The further fact was developed that under pressure a gas decreases at a fixed rate in bulk. A general law, expressing these facts in the phrase that density and elasticity vary inversely with the pressure in a precise ratio, was developed by Boyle and the Frenchman, Mariotte, independently, and bears the name of both of its discoverers. No immediate application of the law to the practical purposes of the worker was made, however, and it is only in recent years that compressed air has been extensively employed as a motive power. Even now it has not proved a great commercial success, because other more economical methods of power production are available. In particular cases, however, it has a certain utility, as a relatively large available source of energy may be condensed into a very small receptacle.
A very striking experiment illustrating the pressure of the air was made by a famous contemporary of Boyle and Mariotte, by the name of Otto von Guericke. He connected an air pump with a large brass sphere, composed of two hemispheres, the edges of which fitted smoothly, but were not connected by any mechanism.Under ordinary conditions the hemispheres would fall apart readily, but von Guericke proved, by a famous public demonstration, that when the air was exhausted in the sphere, teams of horses pulling in opposite directions on the hemispheres could not separate them. This is famous as the experiment of the Magdeburg spheres, and it is often repeated on a smaller scale in the modern physical laboratory, to the astonishment of the tyro in physical experiments.
The first question that usually comes to the mind of anyone who has personally witnessed such an experiment, is the question as to how the human body can withstand the tremendous force to which it is subjected by an atmosphere exerting a pressure of fifteen pounds on every square inch of its surface. The explanation is found in the uniform distribution of the pressure, the influence of which is thus counteracted, and by the fact that the tissues themselves contain everywhere a certain amount of air at the same pressure. The familiar experiment of holding the hand over an exhausted glass cylinder—which experiment is indeed but a modification of the use of the cupping glass above referred to—illustrates very forcibly the insupportable difficulties which the human body would encounter were not its entire surface uniformly subjected to the atmospheric pressure.
At about the time when the scientific experiments with the pressure of gases were being made, practical studies of the effects of masses of air in motionwere undertaken by the Dutch philosopher, Servinus. The use of the windmill in Holland as a means of generating power doubtless suggested to Servinus the possibility of attaching a sail to a land vehicle. He made the experiment, and in the year 1600 constructed a sailing car which, propelled by the wind, traversed the land to a considerable distance, on one occasion conveying a company of which Prince Maurice of Orange was a member. But his experiments have seldom been repeated, and indeed their lack of practical feasibility scarcely needs demonstration.
The utility of the wind, however, in generating the power in a stationary mechanism is familiar to everyone. Windmills were constructed at a comparatively early period, and notwithstanding all the recent progress in the development of steam and electrical power, this relatively primitive so-called prime mover still holds its own in agricultural districts, particularly in its application to pumps. A windmill consists of a series of inclined planes, each of which forms one of the radii of a circle, or spokes of a wheel, to the axle of which a gearing is adjusted by which the power generated is utilized. The wheel is made to face the wind by the wind itself blowing against a sort of rudder which projects from the axis. The wind blowing against the inclined surfaces or vanes of the wheel causes each vane to move in accordance with the law of component forces, thus revolving the wheel as a whole.
WINDMILLS OF ANCIENT AND MODERN TYPES.WINDMILLS OF ANCIENT AND MODERN TYPES.The smaller figures show Dutch windmills of the present day, many of which are identical in structure with the windmills of the middle ages. It will be seen that the sails can be furled when desired to put the mill out of operation. In the mill of modern type (large figure) the same effect is produced by slanting the slats of the wheel.
WINDMILLS OF ANCIENT AND MODERN TYPES.The smaller figures show Dutch windmills of the present day, many of which are identical in structure with the windmills of the middle ages. It will be seen that the sails can be furled when desired to put the mill out of operation. In the mill of modern type (large figure) the same effect is produced by slanting the slats of the wheel.
WINDMILLS OF ANCIENT AND MODERN TYPES.
The smaller figures show Dutch windmills of the present day, many of which are identical in structure with the windmills of the middle ages. It will be seen that the sails can be furled when desired to put the mill out of operation. In the mill of modern type (large figure) the same effect is produced by slanting the slats of the wheel.
It has been affirmed that the Romans had windmills, but "the silence of Vitruvius, Seneca, and Chrysostom, who have spoken of the advantages of the wind, makesthis opinion questionable." It has been supposed by other writers that windmills were used in France in the sixth century, while still others have maintained that this mechanism was unknown in Europe until the time of the Crusades. All that is tolerably certain is that in the twelfth century windmills were in use in France and England. It is recorded that when they began to be somewhat common Pope Celestine III. determined that the tithes of them belonged to the clergy.
The mediæval European windmill was supplied with great sails of cloth, and its picturesque appearance has been made familiar to everyone through the famous tale ofDon Quixote. The modern windmill, acting on precisely the same principle, is a comparatively small affair, comprising many vanes of metal, and constituting a far more practical machine. The great defect of all windmills, however, is found in the fact that of necessity they furnish such variable power, since the force of the wind is incessantly changing. Worst of all, there may be protracted periods of atmospheric calm, during which, of course, the windmill ceases to have any utility whatever. This uneradicable defect relegates the windmill to a subordinate place among prime movers, yet on the other hand, its cheapness insures its employment for a long time to come, and the industry of manufacturing windmills continues to be an important one, particularly in the United States.
The aggregate amount of work accomplished with the aid of the wind is but trifling, compared with that which is accomplished with the aid of water. The supply of water is practically inexhaustible, and this fluid being much more manageable than air, can be made a far more dependable aid to the worker. Every stream, whatever its rate of flow, represents an enormous store of potential energy. A cubic foot of water weighs about sixty-two and a half pounds. The working capacity of any mass of water is represented by one-half its weight into the square of its velocity; or, stated otherwise, by its weight into the distance of its fall. Now, since the interiors of the continents, where rivers find their sources, are often elevated by some hundreds or even thousands of feet, it follows that the working energy expended—and for the most part wasted—by the aggregate water current of the world is beyond all calculation. Meantime, however, a portion of the energy which in the aggregate represents an enormous working power is utilized with the aid of various types of water wheels.
Watermills appear to have been introduced in the time of Mithridates, Julius Cæsar, and Cicero. Strabo informs us that there was a watermill near the residence of Mithridates; and we learn from Pomponius Sabinus, that the first mill seen at Rome was erected on the Tiber, a little before the time of Augustus. That they existed in the time of Augustus is obvious from the description given of them by Vitruvius, and the epigramof Antipater, who is supposed to have lived in the time of Cicero. But though mills driven by water were introduced at this early period, yet public mills did not appear till the time of Honorius and Arcadius. They were erected on three canals, which conveyed water to the city, and the greater number of them lay under Mount Janiculum. When the Goths besieged Rome in 536, and stopped the large aqueduct and consequently the mills, Belisarius appears to have constructed, for the first time, floating mills upon the Tiber. Mills driven by the tide existed at Venice in the year 1046, or at least in 1078.
The older types of water wheel are exceedingly simple in construction, consisting merely of vertical wheels revolving on horizontal axes, and so placed as to receive the weight or pressure of the water on paddles or buckets at their circumference. The water might be allowed to rush under the wheel, thus constituting an under-shot wheel; or more commonly it flows from above, constituting an over-shot wheel. Where the natural fall is not available, dams are employed to supply an artificial fall.
This primitive type of water wheel has been practically abandoned within the last generation, its place having been taken by the much more efficient type of wheel known as the turbine. This consists of a wheel, usually adjusted on a vertical axis, and acting on what is virtually the principle of a windmill. To gain a mental picture of the turbine in its simplest form, one might imagine the propelling screw of a steamship, placed horizontally in a tube, so that the water could rushagainst its blades. The tiny windmills which children often make by twisting pieces of paper illustrate the same principle. Of course, in its developed form the turbine is somewhat elaborated, in the aim to utilize as large a proportion of the energy of the falling water as is possible; but the principle remains the same.
The turbine wheel was invented by a Frenchman named Fourneyron, about three-quarters of a century ago (1827), but its great popularity, in America in particular, is a matter of the last twenty or thirty years. To-day it has virtually supplanted every other type of water wheel. To use any other is indeed a wasteful extravagance, as the perfected turbine makes available more than eighty per cent. of the kinetic energy of any mass of falling water. A turbine wheel two feet in diameter is able to do the work of an enormous wheel of the old type.
Turbine wheels are of several types, one operating in a closed tube to which air has no access, and another in an open space in the presence of air. The water may also be made to enter the turbine at the side or from below, thus serving to support the weight of the mechanism—a consideration of great importance in the case of such gigantic turbines as those that are employed at Niagara Falls, which we shall have occasion to examine in detail in a later chapter.
WATER WHEELS.WATER WHEELS.Fig. 1 shows a model of the so-called breast wheel, a familiar type of water wheel that has been in use since the time of the Romans. Figs. 2 and 3 show similar wheels as used to-day in Belgium. Fig. 4 shows a model of Fourneyron's turbine. This wheel was made in 1837, but the original turbine was introduced by Fourneyron in 1827. The turbine wheel has now almost supplanted the other forms of water wheel except in rural districts.
WATER WHEELS.Fig. 1 shows a model of the so-called breast wheel, a familiar type of water wheel that has been in use since the time of the Romans. Figs. 2 and 3 show similar wheels as used to-day in Belgium. Fig. 4 shows a model of Fourneyron's turbine. This wheel was made in 1837, but the original turbine was introduced by Fourneyron in 1827. The turbine wheel has now almost supplanted the other forms of water wheel except in rural districts.
WATER WHEELS.
Fig. 1 shows a model of the so-called breast wheel, a familiar type of water wheel that has been in use since the time of the Romans. Figs. 2 and 3 show similar wheels as used to-day in Belgium. Fig. 4 shows a model of Fourneyron's turbine. This wheel was made in 1837, but the original turbine was introduced by Fourneyron in 1827. The turbine wheel has now almost supplanted the other forms of water wheel except in rural districts.
The power generated by a revolution of the turbine wheel may, of course, be utilized directly by belts or gearings attached to its axle, or it may be transferred to a distance, with the aid of a dynamo generating electricity. The latter possibility, which has only recentlybeen developed, and which we shall have occasion to examine in detail in connection with our studies of the power at Niagara, gives a new field of usefulness to the turbine wheel, and makes it probable that this form of power will be vastly more used in the future than it has been in the past. Indeed, it would not be surprising were it ultimately to become the prime source of working energy as utilized in every department of the world's work.
Mr. Edward H. Sanborn, in an article on Motive Power Appliances in the Twelfth Census Report of the United States, comments upon the recent advances in the use of water wheels as follows:
"One notable advance in turbine construction has been the production of a type of wheel especially designed for operating under much higher heads of water than were formerly considered feasible for wheels of this type. Turbines are now built for heads ranging from 100 to 1,200 feet, and quite a number of wheels are in operation under heads of from 100 to 200 feet. This is an encroachment upon the field occupied almost exclusively by wheels variously known as the 'impulse,' 'impact,' 'tangential,' or 'jet' type, the principle of which is the impact of a powerful jet of water from a small nozzle upon a series of buckets mounted upon the periphery of a small wheel."
"The impact water wheel," Mr. Sanborn continues, "has come largely into use during the last ten years, principally in the far West, where higher heads of water are available than can be found in other parts of the country. With wheels of this type, exceedingly simplein construction and of comparatively small cost, a large amount of power is developed with great economy under the great heads that are available. With the tremendous water pressure developed by heads of 1,000 feet and upward, which in many cases are used for this purpose, wheels of small diameter develop an extraordinary amount of power. To the original type of impact wheel which first led the field have been added several styles embodying practically the same principle. Considerable study has been given to the designing of buckets with a view to securing free discharge and the avoidance of any disturbing eddies, and important improvements have resulted from the thorough investigation of the action of the water during, and subsequent to, its impact on the buckets. The impact wheel has been adapted to a wide range of service with great variation as to the conditions under which it operates, wheels having been made in California from 30 inches to 30 feet in diameter, and to work under heads ranging from 35 to 2,100 feet, and at speeds ranging from 65 to 1,100 revolutions per minute. A number of wheels of this type have been built with capacities of not less than 1,000 horse-power each."
A few words should be said about the familiar method of transmitting power with the aid of water, as illustrated by the hydrostatic press. This does not indeed utilize the energy of the water itself, but it enables the worker to transmit energy supplied from without, and to gainan indefinite power to move weights through a short distance, with the expenditure of very little working energy. The principle on which the hydrostatic press is based is the one which was familiar to the ancient philosophers under the name of the hydrostatic paradox. It was observed that if a tube is connected with a closed receptacle, such as a strong cask, and cask and tube are filled with water, the cask will presently be burst by the pressure of the water, provided the tube is raised to a height, even though the actual weight of water in the tube be comparatively slight. A powerful cask, for example, may be burst by the water poured into a slender pipe. The result seems indeed paradoxical, and for a long time no explanation of it was forthcoming. It remained for Servinus, whose horseless wagon is elsewhere noticed, to discover that the water at any given level presses equally in all directions, and that its pressure is proportionate to its depth, quite regardless of its bulk. Then, supposing the tube in our experiment to have a cross-section of one square inch, a pressure equal to that in the tube would be transmitted to each square inch of the surface of the cask; and the pressure might thus become enormous.
If, instead of a tube lifted to a height, the same tube is connected with a force pump operated with a lever—an apparatus similar to the fire-engine of Ctesibius—it is obvious that precisely the same effect may be produced; whatever pressure is developed in the piston of the force pump, similar pressure will be transferred to a corresponding area in the surface of the cask or receptacle with which the force pump connects. Inpractise this principle is utilized, where great pressure is desired, by making a receptacle with an enormous piston connecting with the force pump just described.
An indefinite power may thus be developed, the apparatus constituting virtually a gigantic lever. But the principle of the equivalence of weight and distance still holds, precisely as in an actual lever, and while the pressure that may be exerted with slight expenditure of energy is enormous, the distance through which this pressure acts is correspondingly small. If, for example, the piston of the force pump has an area of one square inch, while the piston of the press has an area of several square feet, the pressure exerted will be measured in tons, but the distance through which it is exerted will be almost infinitesimal. The range of utility of the hydrostatic press is, therefore, limited, but within its sphere, it is an incomparable transmitter of energy.
HYDRAULIC PRESS AND HYDRAULIC CAPSTAN.HYDRAULIC PRESS AND HYDRAULIC CAPSTAN.The upper figure shows Bramah's original hydraulic pump and press, now preserved in the South Kensington Museum, London. The machine was constructed in 1796 by Joseph Bramah to demonstrate the principle of his hydraulic press. The discrepancy in size between the small lever worked by hand and the enormous lever carrying a heavy weight gives a vivid impression of the gain in power through the use of the apparatus. The lower figure shows the hydraulic capstan used on many modern ships, in which the same principle is utilized.
HYDRAULIC PRESS AND HYDRAULIC CAPSTAN.The upper figure shows Bramah's original hydraulic pump and press, now preserved in the South Kensington Museum, London. The machine was constructed in 1796 by Joseph Bramah to demonstrate the principle of his hydraulic press. The discrepancy in size between the small lever worked by hand and the enormous lever carrying a heavy weight gives a vivid impression of the gain in power through the use of the apparatus. The lower figure shows the hydraulic capstan used on many modern ships, in which the same principle is utilized.
HYDRAULIC PRESS AND HYDRAULIC CAPSTAN.
The upper figure shows Bramah's original hydraulic pump and press, now preserved in the South Kensington Museum, London. The machine was constructed in 1796 by Joseph Bramah to demonstrate the principle of his hydraulic press. The discrepancy in size between the small lever worked by hand and the enormous lever carrying a heavy weight gives a vivid impression of the gain in power through the use of the apparatus. The lower figure shows the hydraulic capstan used on many modern ships, in which the same principle is utilized.
Moreover, it is possible to reverse the action of the hydraulic apparatus so as to gain motion at the expense of power. A familiar type of elevator is a case in point. The essential feature of the hydraulic elevator consists of a ram attached to the bottom of the elevator and extending down into a cylinder, slightly longer than the height to which the elevator is to rise. The ram is fitting into a cylinder with water-tight packing, or a cut leather valve. Water under high pressure is admitted to the cylinder through the valve at the bottom, and the pressure thus supplied pushes up the ram, carrying the elevator with it, of course. Another valve allows the water to escape, so that ram and elevator may descend, too rapid descent being prevented bythe partial balancing of ram and elevator with weights acting over pulleys. The ram, to the end of which pressure is thus applied, need be but a few inches in diameter. Water pressure is secured by bringing water from an elevation. Such an elevator acts slowly, but is a very safe and in many ways satisfactory mechanism. Such elevators are still used extensively in Europe, but have been almost altogether displaced in America by the electric elevator.
The hydraulic elevator just described is virtually a water engine, the ram acting as piston. A veritable engine, of small size, to perform any species of mechanical work, may be constructed on precisely the same principle, the piston in this case acting in a cylinder similar to that of the ordinary steam engine. Such an engine operates slowly but with great power. It has special utility where it is desirable to apply power intermittently, as in various parts of a dockyard, or in handling guns and ammunition on shipboard. In the former case in particular, it is often inconvenient to use steam power, as steam sent from a central boiler condenses in a way to interfere with its operation. In such a case any number of small water-pressure engines may be operated from a single tank where water is at a high elevation, or where the requisite pressure is secured artificially. In the latter case, the water is kept under pressure by a large piston or ram heavily weighted, the entire receptacle being, of course, of water-tight construction and adapted to withstand pressure. The pump that supplies the tank is ordinarily made to work automatically, ceasing operation as soon as the ramrises to the top of the receptacle, and beginning again whenever, through use of water, the ram begins to descend. Such an apparatus is called an accumulator. Such water engines have come into vogue only in comparatively recent times, being suggested by the steam engine. As already pointed out, their utility is restricted, yet the total number of them in actual use to-day is large, and their share in the world's work is not altogether inconsiderable.
Wecome now to that all-important transformer of power, the steam engine. Everybody knows that steam is a state of water in which, under the influence of heat, the molecules have broken away from the mutual attraction of cohesion, and are flying about at inconceivable speed, rebounding from one another after collision, in virtue of their elasticity, exerting in the aggregate an enormous pressure in every direction. It is this consideration of the intimate character of steam that justifies the title of the present chapter; a title that has further utility as drawing a contrast between the manner of working with which we are now to be concerned, and the various types of workers that we have previously considered.
In speaking of the animal machine and of work accomplished by the air and the water, we have been concerned primarily with masses of matter, possessing and transmitting energy. Of course molecules—since they make up the substance of all matter—could not be altogether ignored, but in the main we have had to do with molar rather than with molecular motion. Now, however, we are concerned with a mechanism in which the molecular activities are directly concerned in performing work.
Even in the aggregate the molecules make up a mere intangible gas, which requires to be closely confined in order that its energy may be made available. Once the molecules have performed their work, they are so changed in their activities that they sink back, as it were, exhausted, into a relatively quiescent state, which enables their latent cohesive forces to reduce them again to the state of a liquid. In a word, we are concerned with the manifestation of energy which depends upon molecular activities in a way quite different from what has been the case with any of the previously considered mechanisms. The tangible manifestation of energy which we term heat is not merely a condition of action and a by-product, as it was in the case of the animal machine; it is the essential factor upon which all the efficiency of the mechanism depends.
It should perhaps be stated that this explanation of the action of the steam engine is a comparatively modern scientific interpretation. The earlier experimenters brought the steam engine to a high state of efficiency, without having any such conception as this of the nature of steam itself. For practical purposes it suffices to note that water when heated takes the form of steam; that this steam has the property of powerful and indefinite expansion; and thirdly, that when allowed to escape from a state of pressure, sudden expansion of the steam cools it sufficiently to cause the recondensation of part of its substance, thus creating a vacuum.
Stated in few words, the entire action of the steam depends upon these simple mechanical principles. The principles are practically applied by permitting thesteam to enter the cylinder where it can act on a piston, to which it gives the thrust that is transmitted to an external mechanism by means of a rod attached to the piston. When the piston has been driven to the end of the desired thrust, the valve is opened automatically, permitting the steam to escape, thus producing a vacuum, and insuring the return thrust of the piston, which is further facilitated, ordinarily, by the admission of steam to the other side of the piston. Practical operation of this mechanism is familiar to everyone, though the marvel of its power and efficiency seems none the less because of its familiarity.
It is not too much to say that this relatively simple device, in its first general application, marked one of the most important turning points in the history of civilization. To its influence, more than to any other single cause, must be ascribed the revolutionary change that came over the character of practical life in the nineteenth century. From prehistoric times till well toward the close of the eighteenth century, there was scarcely any important change in carrying out the world's work. And in the few generations that have since elapsed, the entire aspect of the mechanical world has been changed, the working efficiency of the individual has been largely increased; mechanical tasks have become easy which hitherto were scarcely within the range of human capacity.
Before we go on to the detailed study of the machine which has produced these remarkable results, it is desirable to make inquiry as to the historical development of so important an invention.
The practical steam engine in its modern form dates, as just mentioned, from the latter part of the eighteenth century, and was perfected by James Watt, who is commonly thought of as being its inventor. In point of fact, however, the history of most inventions is duplicated here, as on examination it appears that various forerunners of Watt had been on the track of the steam engine, and some of them, indeed, had produced a workable machine of no small degree of efficiency.
The very earliest experiments were made away back in the Alexandrian days in the second century before the Christian era, the experimenter being the famous Hero, whose work in an allied field was referred to in the preceding chapter. Hero produced—or at least described and so is credited with producing, though the actual inventor may have been Ctesibius—a little toy mechanism, in which a hollow ball was made to revolve on an axis through the agency of steam, which escaped from two bent tubes placed on opposite sides of the ball, their orifices pointing in opposite directions. The apparatus had no practical utility, but it sufficed to establish the principle that heat, acting through the agency of steam, could be made to do mechanical work. Had not the age of Hero been a time of mental stasis, it is highly probable that the principle he had thus demonstrated would have been applied to some more practical mechanism in succeeding generations. As it was, however, nothing practical came of his experiment, and the steam turbine engine was remembered only as a scientific toy.
No other worker continued the experiments, so faras is known, until the time of the great Italian, Leonardo da Vinci, who, late in the fifteenth century, gave a new impulse to mechanical invention. Leonardo experimented with steam, and succeeded in producing what was virtually an explosion engine, by the agency of which a ball was propelled along the earth. But this experiment also failed to have practical result.
Such sporadic experiments as these have no sequential connection with the story of the evolution of the steam engine. The experiments which led directly on to practical achievements were not begun until the seventeenth century. In the very first year of that century, an Italian named Giovanni Battista della Porta published a treatise on pneumatics, in which the idea of utilizing steam for the practical purpose of raising water was expressly stated. The idea of this inventor was put into effect in 1624 by a French engineer and mathematician, Solomon de Caus. He invented two different machines, the first of which required a spherical boiler having an internal tube reaching nearly to the bottom; a fire beneath the boiler produced steam which would force the water in the boiler to a height proportional to the pressure obtained. In the other machine, steam is led from the boiler into the upper part of a closed cistern containing water to be elevated. To the lower portion of the cistern a delivery pipe was attached so that water was discharged under a considerable pressure. This arrangement wasprecisely similar to the apparatus employed by Hero of Alexandria in various of his fountains, as regards the principle of expanding gas to propel water. An important difference, however, consists in the fact that the scheme of della Porta and of de Caus embodied the idea of generating pressure with the aid of steam, whereas Hero had depended merely on the expansive property of air compressed by the water itself.
While these mechanisms contained the germ of an idea of vast importance, the mechanisms themselves were of trivial utility. It is not even clear whether their projectors had an idea of the properties of the condensation of vapor, upon which the working of the practical steam engine so largely depends. This idea, however, was probably grasped about half a century later by an Englishman, Edward Somerset, the celebrated Marquis of Worcester, who in 1663 described in hisCentury of Inventionsan apparatus for raising water by the expansive force of steam. His own account of his invention is as follows:
"An admirable and most forcible way to drive up water by fire; not by drawing or sucking it upwards, for that must be as the philosopher calleth it,intra sphæram activitatis, which is but at such a distance. But this way hath no bounder, if the vessel be strong enough: for I have taken a piece of whole cannon, whereof the end was burst, and filled it three-quarters full of water, stopping and screwing up the broken end, as also the touch-hole; and making a constant fire under it, within twenty-four hours it burst and made a great crack; so that having a way to make my vesselsso that they are strengthened by the force within them, and the one to fill after the other, I have seen the water run like a constant stream, forty feet high: one vessel of water, rarefied by fire, driveth up forty of cold water; and the man that tends the work is but to turn two cocks, that one vessel of water being consumed, another begins to force and refill with cold water, and so successively; the fire being tended and kept constant, which the self-same person may likewise abundantly perform in the interim, between the necessity of turning the said cocks."
It is unfortunate that the Marquis did not give a more elaborate description of this remarkable contrivance. The fact that he treats it so casually is sufficient evidence that he had no conception of the possibilities of the mechanism; but, on the other hand, his description suffices to prove that he had gained a clear notion of, and had experimentally demonstrated, the tremendous power of expansion that resides in steam. No example of his steam pump has been preserved, and historians of the subject have been left in doubt as to some details of its construction, and in particular as to whether it utilized the principle of a vacuum created through condensation of the steam.
This principle was clearly grasped, however, by another Englishman, Thomas Savery, a Cornish mine captain, who in 1698 secured a patent for a steam engine to be applied to the raising of water, etc. A workingmodel of this machine was produced before the Royal Society in 1699. The transactions of the Society contain the following: "June 14th, 1699, Mr. Savery entertained the Royal Society with showing a small model of his engine for raising water by help of fire, which he set to work before them: the experiment succeeded according to expectation, and to their satisfaction."
The following very clear description of Savery's engine is given in the introduction to Beckmann'sHistory of Inventions:
"This engine, which was used for some time to a considerable extent for raising water from mines, consisted of a strong iron vessel shaped like an egg, with a tube or pipe at the bottom, which descended to the place from which the water was to be drawn, and another at the top, which ascended to the place to which it was to be elevated. This oval vessel was filled with steam supplied from a boiler, by which the atmospheric air was first blown out of it. When the air was thus expelled and nothing but pure steam left in the vessel, the communication with the boiler was cut off, and cold water poured on the external surface. The steam within was thus condensed and a vacuum produced, and the water drawn up from below in the usual way by suction. The oval vessel was thus filled with water; a cock placed at the bottom of the lower pipe was then closed, and steam was introduced from the boiler into the oval vessel above the surface of the water. This steam being of high pressure, forced the water up the ascending tube, from the top of which it was discharged, and the oval vessel being thus refilled with steam, the vacuum was againproduced by condensation, and the same process was repeated. By using two oval steam vessels, which would act alternately—one drawing water from below, while the other was forcing it upwards, an uninterrupted discharge of water was produced. Owing to the danger of explosion, from the high pressure of the steam which was used, and from the enormous waste of heat by unnecessary condensation, these engines soon fell into disuse."
THOMAS SAVERY'S STEAM ENGINE.THOMAS SAVERY'S STEAM ENGINE.The principle involved is that of the expansion of steam exerting a propulsive force and its subsequent condensation to produce a vacuum. These are the principles employed in the modern steam engine, but the only use to which they were put in Savery's engine was the elevation of water by suction.
THOMAS SAVERY'S STEAM ENGINE.The principle involved is that of the expansion of steam exerting a propulsive force and its subsequent condensation to produce a vacuum. These are the principles employed in the modern steam engine, but the only use to which they were put in Savery's engine was the elevation of water by suction.
THOMAS SAVERY'S STEAM ENGINE.
The principle involved is that of the expansion of steam exerting a propulsive force and its subsequent condensation to produce a vacuum. These are the principles employed in the modern steam engine, but the only use to which they were put in Savery's engine was the elevation of water by suction.
This description makes it obvious that Savery had the clearest conception of the production of a vacuum by the condensation of steam, and of the utilization of the suction thus established (which suction, as we know, is really due to the pressure of outside air) to accomplish useful work. Savery also arranged this apparatus in duplicate, so that one vessel was filling with water while the other was forcing water to the delivery pipe. This is credited with being the first useful apparatus for raising water by the combustion of fuel. There was a great waste of steam, through imparting heat to the water, but the feasibility of the all-important principle of accomplishing mechanical labor with the aid of heat was at last demonstrated.
As yet, however, the experimenters were not on the track of the method by which power could be advantageously transferred to outside machinery. An effort in quite another direction to accomplish this had been made as early as 1629 by Giovanni Branca, an Italian mathematician, who had proposed to obtain rotary motion by allowing a jet of steam to blow against the vanes of a fan wheel, capable of turning on an axis.In other words, he endeavored to utilize the principle of the windmill, the steam taking the place of moving air. The idea is of course perfectly feasible, being indeed virtually that which is employed in the modern steam turbine; but to put the idea into practise requires special detailed arrangements of steam jet and vanes, which it is not strange the early inventor failed to discover. His experiments appear not to have been followed up by any immediate successor, and nothing practical came of them, nor was the principle which he had attempted to utilize made available until long after a form of steam engine utilizing another principle for the transmission of power had been perfected.
The principle in question was that of causing expanding steam to press against a piston working tightly in a cylinder, a principle, in short, with which everyone is familiar nowadays through its utilization in the ordinary steam engine. The idea of making use of such a piston appears to have originated with a Frenchman, Denis Papin, a scientific worker, who, being banished from his own country, was established as professor of mathematics at the University of Marburg. He conceived the important idea of transmitting power by means of a piston as early as 1688, and about two years later added the idea of producing a vacuum in a cylinder, by cooling the cylinder,—the latter idea being, as we have just seen, the one which Savery put into effect.