At first sight it might seem as if this arrangement rendered nugatory the attempt to take advantage of the rise and fall of the buoy; but it is not so when the relations of the four buoys to one another are considered. Although the frame is free to move up and down upon the uprising shaft, still its inclination to the vertical is determined by the direction of the line drawn from a buoy in the trough of a wave to one on the crest. Inorder to facilitate the free movement, and to render the rocking effect more accurate and free from vibration, sets of wheels running on rails fixed to the beam are of considerable advantage.
The rise and fall of the tides render necessary the adoption of some such compensating device as that which has been indicated. Of course it would be possible to provide for utilising the force generated by a buoy simply moored direct to a ring at the bottom by means of a common chain cable; but this latter would require to be of a length sufficient to provide for the highest possible wave on the top of the highest tide. Then, again, the loose chain at low tide would permit the buoy to drift abroad within a very considerable area of sea surface, and in order to take advantage of the rise and fall on each wave it would be essential to provide at the derrick on the shore end of the wave-power plant very long toothed bands or equivalent devices on a similarly enlarged scale.
By providing three or four chains and moorings, meeting in a centre at the buoy itself but fastened to rings secured to weights at the bottom at a considerable distance apart, the lateral movement might, no doubt, be minimised; and for very simple installationsthis plan, associated with the device of taking a cable from the buoy and turning it several times round a drum on shore, could be used to furnish a convenient source of cheap power. The drum may carry a crank and shaft, which works the spur-wheel and toothed bands as already described, so that no matter at what stage in the revolution of the drum an upward or downward stroke may be stopped, the motion will still be communicated in a continuous rotary form to the fly-wheel.
But the beam and sliding frame, with buoys, give the best practical results, especially for large installations. It is in some instances advisable, especially where the depth of the water at a convenient distance from the shore is very considerable, not to provide a single beam reaching the whole distance to the bottom, but to anchor an air-tight tank below the surface and well beneath the depth at which wave disturbance is ever felt. From this submerged tank, which approximately keeps a steady position in all tides and weathers, the upward beam is attached by a ring just as would be done if the tank itself constituted the bottom.
One main reason for this arrangement is that the resistance of the beam to the water as it rocks backwards and forwards wastes to some extent the power generated by the forceof the waves; and the greater the length of the beam, the longer must be the distance through which it has to travel when the buoys draw it into positions vertical to that of the framework. A thin steel pipe offers less resistance than a wooden beam of equal strength, besides facilitating the use of a simple device for enabling the frame and buoys to slide easily up and down.
The generally fatal defect of those inventions which have been designed in the past with the object of utilising wave-power has arisen from the mistake of placing too much of the machinery in the sea. The device of erecting in the water an adjustable reservoir to catch the wave crests and to use the power derived from them as the water escaped through a water-wheel was patented in 1869. Nearly twenty years later another scheme was brought out depending upon the working of a large pump fixed far under the surface, and connected with the shore so that, when operated by the rising and falling of floats upon the waves, it would drive a supply of water into an elevated reservoir on shore, from which, on escaping down the cliff, the pressure of the water would be utilised to work a turbine.
Earlier devices included the building of amill upon a rocking barge, having weights and pulleys adjusted to run the machinery on board; and also a revolving float so constructed that each successive wave would turn one portion, but the latter would then be held firm by a toothed wheel and ratchet until another impulse would be given to it in the same direction. This plan included certain elements of the simple system already described; but it is obvious that some of its floating parts might with advantage have been removed to the shore end, where they would not only be available for ready inspection and adjustment, but also be out of harm's way in rough weather.
Different wave-lengths, as already explained, correspond to various periods in the pendulous swing of floating bodies. Examples have been cited by Mr. Vaughan Cornish, M. Sc., inKnowledge, 2nd March, 1896, as follows: "A wave-length of fifty feet corresponds to a period of two and a half seconds, while one of 310 feet corresponds to five and a half seconds. It is mentioned that the swing of the steam-shipGreat Easterntook six seconds." Other authorities state that during a storm in the Atlantic the velocity of the wave was determined to be thirty-two miles an hour, and that nine or ten waves were included in eachmile; thus about five would pass in each minute. But in average weather the number of waves to the mile is considerably larger, say, from fifteen to twenty to the mile; and in nearly calm days about double those numbers.
One interesting fact, which gives to wave-power a peculiarly enhanced value as a source of stored wind-power, is that the surface of the ocean—wild as it may at times appear—is not moved by such extremes of agitation as the atmosphere. In a calm it is never so inertly still, and in a storm it is never so far beyond the normal condition in its agitation as is the wind. The ocean surface to some extent operates as the governor of a steam-engine, checking an excess in either direction. In very moderate weather the number of waves to the mile is greatly increased, while their speed is not very much diminished. Indeed the rate at which they travel may even be increased.
This latter phenomenon generally occurs when long ocean rollers pass out of a region of high wind into one of relative calm, the energy remaining for a long time comparatively constant by reason of the multiplication of short, low waves created out of long, high ones. On all ocean coasts the normal conditionof the surface is governed by this law, and it follows that, no matter what the local weather may be at any given time, there is always plenty of power available.
An attempt was made by M. C. Antoine, after a long series of observations, to establish a general relation between the speed of the wind and that of the waves caused by it, the formulæ being published in theRevue Nautique et Colonialein 1879. The rule may be taken as correct within certain limits, although in calm weather, when the condition of the ocean surface is almost entirely ruled by distant disturbances, it has but little relevancy. Approximately, the velocity of wave transmission is seven times the fourth root of the wind-speed; so that when the latter is a brisk breeze of sixteen miles an hour the waves will be travelling fourteen miles an hour, or very nearly as fast as the wind. When, on the other hand, a light breeze of nine miles an hour is driving the waves, the latter, according to the formula, should run about twelve and a half miles an hour; but, in point of fact, the influence of more distant commotion nearly always interferes with this result.
As a matter of experience, the waves on an ocean coast are usually running faster than thewind, and, being so much more numerous in calm than they are in rough weather, they maintain comparatively a uniform sum total of energy. It is obvious that, so far as practical purposes are concerned, three waves of an available height of three feet each are as effective as one of nine feet. If the state of the weather be such that the average wave length is 176 feet there will be exactly thirty waves to the mile, and if the speed be twelve miles an hour—that is to say, if an expanse of twelve miles of waves pass a given point hourly—then 360 waves will pass every sixty minutes, or six every minute. In the wave-power plant as described, each buoy of one hundred tons displacement when raised and depressed, say, three feet by every wave will thus be capable of giving power equal to three times 600, or 1,800 foot-tons per minute.
The unit of nominal horse-power being 33,000 foot-pounds or about fifteen foot-tons per minute, it is evident that each buoy, at its maximum, would be capable of giving about 120 horse-power. Supposing that half of the possible energy were exerted at the forward and half at the backward stroke and that each buoy were always in position to exert its full power upon the uprising shaft without deduction, the total effective duty ofa machine such as has been described would be 480 horse-power. In practice, however, the available duty would probably, according to minor circumstances, be rather more or rather less than 300 horse-power.
The three principal forms of stored power which are now in sight above the horizon of the industrial outlook are the electric storage battery, compressed air, and calcium-carbide. The first of these has come largely into use owing to the demand for a regulated and stored supply of electricity available for lighting purposes. Indeed the storage battery has practically rendered safe the wide introduction of electric lighting, because a number of cells, when once charged, are always available as a reserve in case of any failure in the power or in the generators at any central station; and also because, by means of the storage cells or "accumulators," the amount of available electrical energy can be subdivided into different and subordinate circuits, thus obviating the necessity for the employment of currents of very high voltage and eluding the only imperfectly-solved problem of dividing a current traversing a wire as conveniently as lightinggas is divided by taking small pipes off from the gas mains.
Compressed air for the storage of power has hitherto been best appreciated in mining operations, one of the main reasons for this being that the liberated air itself—apart from the power which it conveyed and stored—has been so great a boon to the miner working in ill-ventilated stopes and drives. The cooling effects of the expansion, after close compression, are also very grateful to men labouring hard at very great depths, where the heat from the country rock would become, in the absence of such artificial refrigeration, almost overpowering. For underground railway traffic exactly the same recommendations have, at one period during the fourth quarter of the nineteenth century, given an adventitious stimulus to the use of compressed air.
Yet it is now undoubted that, even in deep mining, the engineer's best policy is to adopt different methods for the conveyance and storage of power on the one hand, and for the ventilation of the workings on the other. Few temptations are more illusory in the course of industrial progress than those presented by that class of inventions which aim at "killing two birds with one stone". If one object be successfully accomplished it almost invariablyhappens that the other is indifferently carried out; but the most frequent result is that both of them suffer in the attempt to adapt machinery to irreconcilable purposes.
The electric rock-drill is now winning its way into the mines which are ventilated with comparative ease as well as into those which are more difficult to supply with air. It is plain, therefore, that on its merits as a conveyer and storer of power the electric current is preferable to compressed air. The heat that is generated and then dissipated in the compression of any gas for such a purpose represents a very serious loss of power; and it is altogether an insufficient excuse to point to the compensation of coolness being secured from the expansion. Fans driven by electric motors already offer a better solution of the ventilation difficulty, and the advantages on this side are certain to increase rather than to diminish during the next few years.
The electric rock-drill, which can already hold its own with that driven by compressed air, is therefore bound to gain ground in the future. This is a type and indication of what will happen all along the industrial line, the electric current taking the place of the majority of other means adopted for the transmission of power. Even in workshops—where it isimportant to have a wide distribution of power and each man must be able to turn on a supply of it to his bench at any moment—shafting is being displaced by electric cables for the conveyance of power to numerous small motors.
The loss of power in this system has already been reduced to less than that which occurs with shafting, unless under the most favourable circumstances; and in places where the works are necessarily distributed over a considerable area the advantage is so pronounced that hardly any factories of that kind will be erected ten years hence without resort being had to electricity, and small motors as the means of distributing the requisite supplies of power to the spots where they are needed. It was a significant fact that at the Paris Exposition of 1900 the electric system of distribution was adopted.
In regard to compressed air, however, it seems practically certain that, notwithstanding its inferiority to electric storage of power, it is applicable to so many kinds of small and cheap installations that, on the whole, its area of usefulness, instead of being restricted, will be largely increased in the near future. There will be an advance all along the line; and although electric storage will far outstrip compressed air for the purposes of the large manufacturer, the air reservoir will provehighly useful in isolated situations, and particularly for agricultural work.
For example, as an adjunct to the ordinary rural windmill for pumping water, it will prove much more handy and effective than the system at present in vogue of keeping large tanks on hand for the purpose of ensuring a supply of water during periods of calm weather. Regarding a tank of water elevated above the ground and filled from a well as representing so much stored energy, and also comparing this with an equal bulk of air compressed to about 300 pounds pressure to the square inch, it would be easy to show that—unless the water has been pumped from a very deep well—the power which its elevation indicates must be only a small fraction of that enclosed in the air reservoir.
It will be one great point in favour of compressed air, as a form of stored energy for the special purpose of pumping, that by making a continuous small flow of air take the place of the water at the lowest level in the upward pipe, it is possible to cause it to do the pumping without the intervention of any motor.
One means of effecting this may be simply indicated. The air under pressure is admitted from a very small air pipe and the bubbles, as they rise, fill the hollow of an inverted ironcup rising and falling on a bearing like a hinge. Above and beneath the chamber containing this cup are valves opening upwards and similar to those of an ordinary force or suction pump. The cup must be weighted with adjustable weights so that it will not rise until quite full of air. When that point is reached the stroke is completed, the air having driven upwards a quantity of water of equal bulk with itself, and, as the cup falls again by its own weight, the vacuum caused by the air escaping upwards through the pipe is filled by an inrush of water through the lower valve. The function of the upper valve, at that time, is to keep the water in the pipe from falling when the pressure on the column is removed. The expansive power of the air enables it to do more lifting at the upper than at the lower level, so that a larger diameter of pipe can be used at the former place.
Cheap motors working on the same principle—that is to say through the upward escape of compressed air, gas or vapour filling a cup and operating it by its buoyancy, or turning a wheel in a similar manner—will doubtless be a feature in the machine work of the future; and for motors of this description it is obvious that compressed air will be very useful as the form of power-storage. Excepting under veryspecial conditions, steam is not available for such a purpose, seeing that it condenses long before it has risen any material distance in a column of cold water.
"The present accumulator," remarked Prof. Sylvanus P. Thompson in the year 1881, referring to the Faure storage batteries then in use, "probably bears as much resemblance to the future accumulator as a glass bell-jar used in chemical experiments for holding gas does to the gasometer of a city gasworks, or James Watt's first model steam-engine does to the engines of an Atlantic steamer." When Faure, having in 1880 improved upon the storage battery of Planté, sent his four-cell battery from Paris to Glasgow, carrying in it stored electrical energy, it was found to contain power equal to close upon a million foot-pounds, which is about the work done by a horse-power during the space of half an hour. This battery weighed very nearly 75 lb. It nevertheless represented an immense forward step in the problem of compressing a given quantity of potential power into a small weight of accumulator.
The progress made during less than twenty years to the end of the century may be estimated from the conditions laid down by the Automobile Club of Paris for the competitivetest of accumulators applicable to auto-car purposes in 1899. It was stipulated that five cells, weighing in all 244 lb., should give out 120 ampere-hours of electric intensity; and that at the conclusion of the test there should remain a voltage of 1·7 volt per cell.
Very great improvements in the construction of electric accumulators are to be looked for in the near future. Hitherto the average duration of the life of a storage cell has not been more than about two years; and where impurities have been present in the sulphuric acid, or in the litharge or "minium" employed, the term of durability has been still further shortened. It must be remembered that while the principal chemical and electrical action in the cell is a circular one,—that is to say, the plates and liquids get back to the original condition from which they started when beginning work in a given period,—there is also a progressive minor action depending upon the impurities that may be present. Such a reagent, for instance, as nitric acid has an extremely injurious effect upon the plates.
During the first decade after Planté and Faure had made their original discoveries, the main drawback to the advancement of the electric accumulator for the storage of power owed its existence to the lack of precise knowledge,among those placed in charge of storage batteries, as to the destructive effects of impurities in the cells. It is, however, now the rule that all acids and all samples of water used for the purpose must be carefully tested before adoption, and this practice, in itself, has greatly prolonged the average life of the accumulator cell.
The era of the large electric accumulator of the kind foreshadowed by Prof. Sylvanus P. Thompson has not yet arrived, the simple reason being that electric power storage—apart from the special purposes of the subdivision and transmission for lighting—has not yet been tried on a large scale. For the regulation and graduation of power it is exceedingly handy to be able to "switch-on" a number of small accumulator cells for any particular purpose; and, of course, the degree of control held in the hands of the engineer must depend largely on the smallness of each individual cell, and the number which he has at command. This fact of itself tends to keep down the size of the storage cell which is most popular.
But when power storage by means of the electric accumulator really begins in earnest the cells will attain to what would at present be regarded as mammoth proportions; and the special purpose aimed at in each instance ofpower installation will be the securing of continuity in the working of a machine depending upon some intermittent natural force. Windmills are especially marked out as the engines which will be used to put electrical energy into the accumulators. From these latter again the power will be given out and conveyed to a distance continuously.
High ridges and eminences of all kinds will in the future be selected as the sites of wind-power and accumulator plants. In the eighteenth century, when the corn from the wheat-field required to be ground into flour by the agency of wind-power, it was customary to build the mill on the top of some high hill and to cart all the material laboriously to the eminence. In the installations of the future the power will be brought to the material rather than the material to the power. From the ranges or mountain peaks, and also from smaller hills, will radiate electrical power-nerves branching out into network on the plains and supplying power for almost every purpose to which man applies physical force or electro-chemical energy.
The gas-engine during the twentieth century will vigorously dispute the field against electrical storage; and its success in the struggle—so far as regards its own particular province—will beenhanced owing to the fact that, in some respects, it will be able to command the services of electricity as its handmaid. Gas-engines are already very largely used as the actuators of electric lighting machinery. But in the developments which are now foreshadowed by the advent of acetylene gas the relation will be reversed. In other words, the gas-engine will owe its supply of cheap fuel to the electric current derived at small expense from natural sources of power.
Calcium carbide, by means of which acetylene gas is obtained as a product from water, becomes in this view stored power. The marvellously cheap "water-gas" which is made through a jet of steam impinging upon incandescent carbons or upon other suitable glowing hot materials will, no doubt, for a long time command the market after the date at which coal-gas for the generation of power has been partially superseded.
But it seems exceedingly probable that a compromise will ultimately be effected between the methods adopted for making water-gas and calcium carbide respectively, the electric current being employed to keep the carbons incandescent. When power is to be sold in concrete form it will be made up as calcium carbide, so that it can be conveyed to anyplace where it is required without the assistance of either pipes or wires. But when the laying of the latter is practicable—as it will be in the majority of instances—the gas for an engine will be obtainable without the need for forcing lime to combine with carbon as in calcium carbide.
Petroleum oil is estimated to supply power at just one-third the price of acetylene gas made with calcium carbide at a price of £20 per ton. This calculation was drawn up before the occurrence of the material rise in the price of "petrol" in the last year of the nineteenth century; while, concurrently, the price of calcium carbide was falling. A similar process will, on the average, be maintained throughout each decade; and, as larger plants, with cheaper natural sources of energy, are brought into requisition, the costs of power, as obtained from oil and from acetylene gas, will more and more closely approximate, until, in course of time, they will be about equal; after which, no doubt, the relative positions will be reversed, although not perhaps in the same ratio. Time is all on the side of the agent which depends for its cheapness of production on the utilisation of any natural source of power which is free of all cost save interest, wear and tear, and supervision.
Even the steam-engine itself is not exempt from the operation of the general law placing the growing advantage on the side of power that is obtainable gratis. One cubic inch of water converted into steam and at boiling point will raise a ton weight to the height of one foot; and the quantity of coal of good quality needed for the transformation of the water is very small. One pound of good coal will evaporate nine pounds of water, equal to about 250 cubic inches, this doing 250 foot-tons of work. But Niagara performs the same amount of work at infinitely less cost. However small any quantity may be, its ratio to nothing is infinity.
It has been the custom during the nineteenth century to institute comparisons between the marvellous economy of steam power and the expensive wastefulness of human muscular effort. For instance, the full day's work of an Eastern porter, specially trained to carry heavy weights, will generally amount to the removal of a load of from three to five hundred-weight for a distance of one mile; but such a labourer in the course of a long day has only expended as much power as would be stored up in about five ounces of coal.
Still the fact remains that one of the greatest problems of the future is that which concernsthe reduction in the cost of power. Hundreds of millions of the human race pass lives of a kind of dull monotonous toil which develops only the muscular, at the expense of the higher, faculties of the body; they are almost entirely cut off from social intercourse with their fellow-men, and they sink prematurely into decrepitude simply by reason of the lack of a cheap and abundant supply of mechanical power, ready at hand wherever it is wanted. Scores of "enterprises of great pith and moment" in the industrial advancement of the world have to be abandoned by reason of the same lack. In mining, in agriculture, in transport and in manufacture the thing that is needful to convert the "human machine" into a more or less intelligent brainworker is cheaper power. All the technical education in the world will not avail to raise the labourer in the intellectual scale if his daily work be only such as a horse or an engine might perform.
The transmission of power through the medium of the electric current will naturally attain its first great development in the neighbourhoods of large waterfalls such as Niagara. When the manufacturers within a short radius of the source of power in each case have begun to fully reap the benefit due to cheap power, competition will assert itself in many differentways. The values of real property will rise, and population will tend to become congested within the localities' served.
It will be found, however, that facilities for shipment will to a large extent perpetuate the advantage at present held by manufactories situated on ports and harbours; and this, of course, will apply with peculiar force to the cases of articles of considerable bulk. Where a very great deal of power is needed for the making of an article or material of comparatively small weight and bulk proportioned to its value—such for instance as calcium carbide or aluminium—the immediate vicinity of the source of natural power will offer superlative inducements. But an immense number of things lie between the domains of these two classes, and for the economical manufacture of these it is imperative that both cheap power and low wharfage rates should be obtainable.
An increasingly intense demand must thus spring up for systems of long distance transmission, and very high voltage will be adopted as the means of diminishing the loss of power due to leakage from the cables. Similarly the "polyphase" system—which is eminently adapted to installations of the nature indicated—must demand increasing attention.
Taking a concrete example, mention may bemade of the effects to be expected from the proposed scheme for diverting some of the headwaters of the Tay and its lakes from the eastern to the western shores of Scotland and establishing at Loch Leven—the western inlet, not the inland lake of that name—a seaport town devoted to manufacturing purposes requiring very cheap supplies of power. It is obvious that the owners of mills in and around Glasgow, and only forty or fifty miles distant, will make the most strenuous exertions to enable them to secure a similar advantage.
It is already claimed that with the use of currents of high voltage for carrying the power, and "step-down transformers" converting these into a suitable medium for the driving of machinery, a fairly economical transmission can be ensured along a distance of 100 miles. It therefore seems plain that the natural forces derived from such sources as waterfalls can safely be reckoned upon as friends rather than as foes of the vested interests of all the great cities of the United Kingdom.
The possibilities of long distance transmission are greatly enhanced by the very recent discovery that a cable carrying a current of high voltage can be most effectually insulated by encasing it in the midst of a tube filled with wet sawdust and kept at a lowtemperature, preferably at the freezing point of water.
Wireless transmission of a small amount of power has been proved to be experimentally possible. In the rarefied atmosphere at a height of five or ten miles from the earth's surface, electric discharges of very high voltage are conveyed without any other conducting medium than that of the air. By sending up balloons, carrying suspended wires, the positions of despatch and of receipt can be so elevated that the resistance of the atmosphere can be almost indefinitely diminished. In this way small motors have been worked by discharges generated at considerable distances, and absolutely without the existence of any connection by metallic conductors. Possibilities of the exportation of power from suitable stations—such as the neighbourhoods of waterfalls—and its transmission for distances of hundreds or even thousands of miles have been spoken of in relation to the industrial prospects of the twentieth century.
Comparing any such hypothetical system with that of sending power along good metallic conductors, there is at once apparent a very serious objection in the needless dispersion of energy throughout space in every direction. If a power generator by wireless transmission,without any metallic connection, can work one motor at a distance of, say, 1,000 miles, then it can also operate millions of similar possible motors situated at the same distance; and by far the greater part of its electro-motive force must be wasted in upward dispersion.
The analogy of the wireless transmitter of intelligence may be misleading if applied to the question of power. The practicability of wireless telegraphy depends upon the marvellous susceptibility of the "coherer," which enables it to respond to an impulse almost infinitesimally small, certainly very much smaller than that despatched by the generator from the receiving station. From this it follows, as already stated, that the analogy of apparatus designed merely for the despatch of intelligence by signalling cannot safely be applied to the case of the transmission of energy.
Making all due allowances for the prospects of advance in minimising the resistance of the atmosphere, it must nevertheless be remembered that any wireless system will be called upon to compete with improved means of conveying the electric current along metallic circuits. Electrical science, moreover, is only at the commencement of its work in economising the cost of power-cables.
The invention by which one wire can beused to convey the return current of two cables very much larger in sectional area is only one instance in point. The two major cables carry currents running in opposite directions, and as these currents are both caused to return along the third and smaller wire their electro-motive forces balance one another, with the result that the return wire needs only to carry a small difference-current. The return wire, in fact, is analogous to the Banking Clearing House, which deals with balances only, and which therefore can sometimes adjust business to the value of many millions with payments of only a few thousands. Later on it may fairly be expected that duplicate and quadruplicate telegraphy will find its counterpart in systems by which different series of electrical impulses of high voltage will run along a wire, the one alternating with the other and each series filling up the gaps left between the others.
The steam-turbine is the most clearly visible of the revolutionary agencies in motors using the artificial sources of power. In the first attempts to introduce the principle the false analogy of the water-turbine gave rise to much waste of inventive energy and of money; but the more recent and more distinctly successful types of machine have been constructed with a clear understanding that the windmill is the true precursor of the steam-turbine. It is clearly perceived that, although it may be convenient and even essential to reduce the arms to pigmy dimensions and to enclose them in a tube, still the general principle of the machine must resemble that of a number of wind motors all running on the same shaft.
It has been proved, moreover, that this multiplicity of minute wheels and arms has a very distinct advantage in that it renders possible the utilisation of the expansive power of steam. The first impact is small in area but intense in force, while those arms whichreceive the expanded steam further on are larger in size as suited to making the best use of a weaker force distributed over a greater amount of space.
The enormous speed at which steam under heavy pressure rushes out of an orifice was not duly appreciated by the first experimenters in this direction. To obtain the best results in utilising the power from escaping steam there must be a certain definite proportion between the speed of the vapour and that of the vane or arm against which it strikes. In other words, the latter must not "smash" the jet, but must run along with it. In the case of the windmill the ratio has been stated approximately by the generalisation that the velocity of the tips of the sails is about two and a half times that of the wind. This refers to the old style of windmill as used for grinding corn.
The steam turbine must, therefore, be essentially a motor of very great initial speed; and the efforts of recent inventors have been wisely directed in the first instance to the object of applying it to those purposes for which machinery could be coupled up to the motor with little, if any, necessity for slowing down the motion through such appliances as belting, toothed wheels, or other forms ofintermediate gearing. The dynamo for electric lighting naturally first suggested itself; but even in this application it was found necessary to adopt a rate of speed considerably lower than that which the steam imparts to the turbine; and, unfortunately, it is exactly in the arrangement of the gear for the first slowing-down that the main difficulty comes in.
Nearly parallel is the case of the cream separator, to which the steam-turbine principle has been applied with a certain degree of success. By means of fine flexible steel shafts running in bearings swathed in oil it has been found possible to utilise the comparatively feeble force of a small steam jet operating at immense speed to produce one of much slower rate but enormously greater strength. Some success has been achieved also in using the principle not only for cream separators, which require a comparatively high velocity, but for other purposes connected with the rural and manufacturing industries.
An immense forward stride, however, was made when the idea was first conceived of a steam-turbine and a water-turbine being fixed on the same shaft and the latter being used for the propulsion of a vessel at sea. In this case it is obvious that, by a suitable adjustment of the pitch of screw adopted in bothcases, a nice mathematical agreement between the vapour power and the liquid application of that power can be ensured.
All previous records of speed have been eclipsed by the turbine-driven steamers engined on this principle. Through the abolition of the principal causes of excessive vibration—which renders dangerous the enlargement of marine reciprocating engines beyond a certain size—the final limit of possible speed has been indefinitely extended. The comfort of the passenger, equally with the safety of the hull, demands the diminution of the vibration nuisance in modern steamships, and whether the first attempts to cater for the need by turbine-engines be fully successful or not, there is no doubt whatever that the fast mail packets of the future will be driven by steam-engines constructed on a system in which the turbine principle will form an important part.
Further applications will soon follow. It is clear that if the steam-turbine can be advantageously used for the driving of a vessel through the water, then, conversely, it can be similarly applied to the creation of a current of water or of any other suitable liquid. This liquid-current, again, is applicable to the driving of machinery at any rate that may be desired. In this view the slowing-downprocess, which involves elaborate and delicate machinery when accomplished in the purely mechanical method, can be much more economically effected through the friction of fluid particles.
One method of achieving this object is an arrangement in which the escaping steam drives a turbine-shaft running through a long tube and passing into the water in a circular tank, in which, again, the shaft carries a spiral or turbine screw for propelling the water. The arrangement, it will be seen, is strictly analogous to that of the steam-turbine as used in marine propulsion, the shaft passing through the side of the tank just as it does through the stern of the vessel.
One essential point, however, is that the line of the shaft must not pass through the centre of the circular tank, but must form the chord of an arc, so that when the water is driven against the side by the revolution of the screw it acts like a tangential jet. Practically the water is thus kept in motion just as it would be if a hose with a strong jet of water were inserted and caused to play at an obtuse angle against the inner side.
Motion having been imparted to the fluid in the tank, a simple device such as a paddle-wheel immersed at its lower end, may beadopted for taking up the power and passing it on to the machinery required to be actuated. By setting both the shaft carrying the vanes for the steam-turbine and the screw for the propulsion of the water at a downward inclination it becomes practicable to drive the fluid without requiring any hole in the tank; and in this case the latter may be shaped in annular form and pivoted so that it becomes a horizontal fly-wheel. Obstructing projections on the inside periphery of the annular tank assist the water to carry the latter along with it in its circular motion.
For small steam motors, particularly for agricultural and domestic purposes, the turbine principle is destined to render services of the utmost importance. The prospect of its extremely economical construction depends largely upon the fact that, with the exception of two or three very small bearings carrying narrow shafts, it contains no parts demanding the same fine finish as does the cylinder of a reciprocating engine. It solves in a very simple manner the much-vexed problem of the rotary engine, upon which so much ingenuity has been fruitlessly exercised. The steam-turbine also has shown that, for taking advantage of the generation and the expansive power of steam, there is no absolute necessity forincluding a steam-tight chamber with moving parts in the machine.
For very small motors suitable for working fans and working other household appliances, the use of a jet of steam, applied directly to drive a small annular fly-wheel filled with mercury—without the intervention of any turbine—will no doubt prove handy. But in the economy of the future such appliances will take the place of electrical machinery only in exceptional situations.
One promising use of the turbine or steam-jet—used to propel a fly-wheel filled with liquid as described—has for its object the supply of the electric light in country houses. In this case the fly-wheel is fitted, on its lower side, to act as the armature of a dynamo, and the magnets are placed horizontally around it.
The full effective power from a jet of steam is not communicated to a dynamo for electric lighting or other purposes unless there be a definite ratio between the speeds of the turbine and of the armature respectively. This may be conveniently provided for, with more precision and in a less elaborate way than that which has just been described, if the steam jet be made to drive a vertically pendant turbine, the lower extremity of which, carryingvery small horizontal paddles, must be inserted into the centre of a circular tank.
The principle upon which the reduction of speed necessary for the dynamo is then effected depends upon the fact that in a whirlpool the liquid near the centre runs nearly as fast as that on the outer periphery, and therefore—the circles being so very much smaller—the number of revolutions effected in a given time is much greater. Thus a steam jet turning a pendant turbine—dipping into the middle of the whirlpool and carrying paddles—at an enormously high speed may be made to impart motion to the water in a circular tank (or, if desired, to the tank itself) at a very much slower rate; the amount of the reduction, of course, depending mainly on the ratio between the diameter of the tank and the length of the small paddles at the centre setting the liquid in motion.
For special purposes it is best to substitute a spherical for an ordinary circular tank and the size may be greatly diminished by using mercury instead of water. The sphere is complete, excepting for a small aperture at the top for the admission of the steel shaft of the steam-driven turbine. No matter how high may be the speed, the liquid cannot be thrown out from a spherical revolving receptacle constructed in this way. Moreover, the mercuryacts not only as a transmitter of the power from the turbine to the purpose for which it is wanted, but also as a governor. Whenever the speed becomes so great as to throw the liquid entirely into the sides of the sphere—so that the shaft and paddles are running free of contact with it in the middle—the machine slows down, and it cannot again attain full speed until the same conditions recur.
The rate of speed which may be worked up to as a maximum is determined by the position of the paddle-wheel, which is adjustable and floats upon the liquid although controlled in its circular motion by the shaft which passes through a square aperture in it and also a sleeve extending upward from it. The duty of the latter is to economise steam by cutting off the jet as soon as, by its rapidity of motion, the paddle-wheel has thrown the mercury to the sides to such an extent as to sink to a certain level in the centre.
Cheap motors coupled with cheap dynamos will, in the twentieth century, go far towards lightening the labours of millions whose toil is at present far too much of a mere mechanical nature. The dynamo itself, however, requires to be greatly reduced in first cost. Particularly it is necessary that the expense involved in drawing the wire, insulating it, and windingmachines with it, should be diminished. This will no doubt be partly accomplished by the electrolytic producers of copper when once they get properly started on methods of depositing thin strips or wires of tough copper on to sheets of insulating material for wrapping round the magnets and other effective parts intended for dynamos. There is no fundamental reason which forbids that when electro deposition is resorted to for the recovery of a metal from its ore it should be straightway converted to the shape and to the purpose for which it is ultimately intended. This consideration has presented itself to the minds of some of the manufacturers of aluminium, who make many articles intended for household use electrolytically; and it must affect many other trades which are concerned in the output and in the working-up of metals readily susceptible of deposition—more particularly such as copper.
The familiar aneroid barometer furnishes a hint for another convenient form of small steam-engine. In seeking to cheapen machinery of this class it is of the utmost importance that the necessity for boring out cylinders and for planing and other expensive work should be avoided. In the aneroid barometer a shallow circular box is fitted with a cover,which is corrugated in concentric circles, and the pressure of the superincumbent air is caused to depress the centre of this cover through the device of partially exhausting the box of air and thus diminishing the internal resistance. To the slightly moving middle part of the cover is affixed a lever which actuates, after some intermediate action, the hand which moves on the dial to indicate, by its record of variations in the weight of the atmosphere, what the prospect of the weather may be.
In the aneroid form of the steam-engine the cylinder is immensely widened and flattened, and the broad circular lid, with its spiral corrugations, takes the place of the piston. The rod, which acts virtually as a piston-rod, is hollow, and it works into a bearing which permits the steam to escape when the extreme point of the stroke has been reached into a separate condensing chamber kept cool with water. The boiler itself, with corrugated top, may take the place of the cylinder.
In some respects this little machine represents a retrograde movement, even from Watt's original engine with its separate condenser; but its extreme economy of first cost recommends it to poor producers. In the near future no country homestead will be withoutits power installation of one kind or another, and there is room for many types of cheap motors.
A motor like the steam-turbine is evidently the forerunner of other engines designed to utilise the force of an emission jet of vapour or gas. There are very many processes in which gases generated by chemical combinations are permitted to escape without performing any services, not even that of giving up the energy which they may be made to store up when held in compression in a closed vessel.
The reciprocating forms found suitable for steam and gas engines are hardly adaptable for experiments in the direction of economising this source of power, one fatal objection in the majority of cases being the corrosive effects of the gases generated upon the insides of cylinders and other working parts. As soon as the force of the emission jet can be applied as a factor in giving motive power, the fact that no close-fitting parts are required for the places upon which the line of force impinges will alter the conditions of the whole problem. In the centrifugal sand pump, as now largely used for raising silt from rivers and harbours, the serious corrosive action of the jet of sand and water upon the inside of the pump has been successfully overcome byfacing the metal with indiarubber; but nothing of the kind could have been done if the working of the apparatus had depended on the motion of close-fitting parts, as in the ordinary suction or lift pump.
As an instance of the class of work for which gaseous jets, for driving turbines or similar forms of motor, may perform useful services the case of farm-made superphosphate of lime may be cited. By subjecting bones to the action of sulphuric acid the farmer may manufacture his own phosphatic manures for the enrichment of his land. But the carbonic dioxide and other gases generated as the result of the operation are wasted. Therefore it at present pays better to carry the bones to the sulphuric acid than to reverse the procedure by conveying the acid to the farm, where the bones are a by-product.
So bulky are the latter, however, that serious waste of labour is involved in transporting them for long distances. Calculations made out by the experts of various state agricultural stations show that, as a general rule, it is now cheaper for the farmer to buy his superphosphates ready made than to make them on his farm. The difference in some cases, however, is not great; and only a comparative trifle would be needed in order toturn the balance. This may probably be found in the economic value of the service rendered by a turbine-engine or other device for utilising the expansive power of the gases which are driven from the constituents of the bones by the action of the sulphuric acid.
For pumping water and other ordinary farm operations the chemical gas-engine will prove very handy; and the great point in its favour will be that instead of useless cinders the refuse from it will consist of the most valuable compost with which the farmer can dress the soil. Enamelled iron will be employed for the troughs in which the bones and acid will be mixed, and a cover similar to that placed over a "Papin's digester" will be clamped to the rim all round, the gases being liberated only in the form of a jet used for driving machinery.
For very small motors, applicable specially to domestic purposes such as ventilation, there is one source of power which, in all places within the reticulation areas of waterworks, may be had practically for nothing. Probably when the owners of water-supply works realise that they have command of something which is of commercial value, although hitherto unnoticed, they will arrange to sell not only the water which they supply,but also the power which can be generated by its escape when utilised and by the variations in the pressure from hour to hour and even from minute to minute.
The latter, for such purposes as ventilation, for instance, will no doubt come to the front sooner than the intermittent power now wasted by the outflowing of water—a power which is comparatively too small an item in most cases to compensate for the outlay and trouble of arranging for the storage of energy. But in the case of the variation in the pressure, without any escape of water at all, no such disability appears. Experiments conducted in several of the larger cities of England with various types of water meters—which are really motors on a small scale—have proved the practicability of obtaining a source of constant power from what may be termed the ebb and the flow of pressure within the pipes of a water supply system.
At every hour of the day there is a marked variation in the quantity of water that is being drawn away by consumers, and consequently a rise and fall in the degree of pressure recorded by the meter. In an apparatus for converting the power derivable from this source to useful purposes something on a very small scale analogous to that which has alreadybeen described in connection with utilising the rise and fall of a wave will be found serviceable. A small spur-wheel is gripped on two sides by two metal laths, with edges serrated like those of saws, and held against the wheel by gentle pressure. Every movement of the two saws—whether backwards or forwards—is then responded to by a continuous circular motion of the wheel, with the sole exception of those movements which may be too small in extent to include even as much as a single tooth of the wheel. On this account it is important that the teeth should be made as numerous as possible consistently with the amount of pressure which they may have to bear.
Resort may be had to the principle of the aneroid barometer in order to secure from the water within the pipe-system the energy by which these saw-like bands are driven up and down with reciprocal motion. A very shallow circular tank in the shape of a watch is in communication with the water in the pipes, and its top or covering is composed of a concentrically-corrugated sheet of finely tempered steel. At the centre of this is fixed the guide which pushes and pulls the saw-like laths. Every rise and fall in the pressure of the water now effects a movement of the spur-wheel,and the latter may conveniently be connected with the strong spring of a clockwork attachment, so that the water pressure is really used for winding up a clockwork ventilating-fan.
In the making of cheap steam and gas engines, as well as in machine work generally, rapid progress will be made when the possibilities of producing hard and smooth wearing surfaces without the need for cutting and filing rough-cast metal have been fully investigated. Many parts of machinery will be electro-deposited—like the small articles already mentioned—in aluminium or hard copper at the metallurgical works where ore is being treated for the recovery of metal, or even at the mines themselves.
Side by side with this movement there will be one for developing the system of stamping mild steel and then tempering it. At the same time also the behaviour of various metals and alloys, not only in the cold state but also at the critical point between melting and solidification, will be much more carefully studied so as to take advantage of every means whereby accurately shaped articles may be made and finished in the casting. It has been found, for example, that certain kinds of type metal, if placed under very heavy pressureat the moment when passing from the liquid to the solid condition, not only take the exact form of the mould in which they are placed, but become extremely hard by comparison with the same alloy if permitted to solidify without pressure.
The example of the cheap watch industry may be cited to convey an idea of the immensely important revolution which will take place in the production of both small and large prime-motors when all the possibilities of electrotyping, casting, and stamping the various wearing parts true to shape and size have been fully exploited. An accurate timekeeper is now practically within the reach of all; and in the twentieth century no one who requires a small prime motor to do the rough work about home or farm will be compelled to do without it by reason of poverty—unless, perhaps, he is absolutely destitute and a fit subject for public charity.
Many domestic industries which were crushed out of existence during the early part of the nineteenth century will therefore be resuscitated. The dear steam-engine created the factory system and brought the operatives to live close together in long rows of unsightly dwellings, but the cheap engine, in conjunction with the motor driven bytransmitted electricity, will give to the working people comparative freedom again to live where they please, and to enjoy the legitimate pleasures both of town and of country.
The existing keen motor-car rivalry presents one of the most interesting and instructive mechanical problems which are left still unsolved by the close of the nineteenth century. The question to be determined is not so much whether road locomotion by means of mechanical power is practicable and useful, for, of course, that point has been settled long ago; indeed it would have been recognised as settled years before had it not been for the crass legislation of a quarter of a century since which deliberately drove the first steam-motors off the road in order to ensure the undisturbed supremacy of horse traffic. The real point at issue is whether a motor can be made which shall furnish power for purposes of road locomotion as cheaply and conveniently as is already done for stationary purposes.
Horse traction, although extremely dear, possesses one qualification which until the present day has enabled it to outdistance its mechanical competitors upon ordinary roads.This is its power of adapting itself, by special effort, to the exigencies caused by the varying nature of the road. Watch a team of horses pulling a waggon along an undulating highway, with level stretches of easy going and here and there a decline or a steep hill. There is a continual adjustment of the strain which each animal puts upon itself according to the character of the difficulties which must be surmounted, the effort varying from nothing at all—when going down a gentle decline—up to the almost desperate jerk with which the vehicle is taken over some stony part right on the brow of an eminence. The whip cracks and by threats and encouragements the driver induces each horse to put forth, for one brief moment, an effort which could not be sustained for many minutes save at the peril of utter exhaustion.
When the unit of nominal horse-power was fixed at 33,000 foot-pounds per minute the work contemplated in the arbitrary standard was supposed to be such as a horse could go on performing for several hours. It was, of course, well recognised that any good, upstanding horse, if urged to a special effort, could perform several times the indicated amount of work in a minute.
Nevertheless the habit of reckoning steam-powerin terms of a unit drawn from the analogy of the horse undoubtedly tended for many years to obscure the essential difference between the natures of the two sources of power. Railroads were built with the object of rendering as uniform as possible the amount of power required to transport a given weight of goods or passengers over a specified distance; and consequently the application of the steam-engine to traffic conducted on the railway line was a success. Many inventors at once jumped to the conclusion that, by making some fixed allowance for the greater roughness of an ordinary road, they would be able to construct a steam-traction engine that would suit exactly for road traffic. In a rough and rudimentary way an attempt to provide for the special effort required at steep or stony places was made by the introduction of a kind of fly-wheel of extraordinary weight proportionate to the size of the engine; and the same object was aimed at by increasing the power of the engine to somewhere near the limit of the possible special requirements. The consequence was the evolution of an immensely ponderous and wasteful machine, which for some years only held its ground within the domain of the heavy work of roadmaking. As a means of road traction the steam-engine was for half a century almostentirely discomfited and routed by horse-power, partly owing to this mechanical defect and partly, as we have seen, through legislative partisanship.
The explosive type of engine was next called into requisition to do battle against the living competitor of the engineer's handiwork. Petroleum and alcohol, when volatilised and mixed with air in due proportion, form explosive mixtures which are much more nearly instantaneous in their action than an elastic vapour like steam held under pressure in a boiler, and liberated to perform its work by comparatively slow expansion. The petroleum engine, as applied to the automobile, does its work in a series of jerks which provide for the unequal degrees of power required to cope with the unevenness of a road.
As against this, however, there are certain grave defects, due mainly to the use of highly inflammable oils vapourised at high temperatures; and these have impressed a large proportion of engineers with a belief that, in the long run, either electricity or steam will win the day. Storage batteries are well adapted for meeting the exigencies of the road, just as they are for those of tramway traffic, because, as soon as an extra strain is to be met, there is always the resource of coupling up freshbatteries held in reserve—a process which amounts to the same as yoking new horses to the vehicle in order to take it up a hill. In practice, however, it is found that the jerky vibratory motion of the gasoline automobile provides for this in a way almost as convenient, although not so pleasant.
The chance of the steam-engine being largely adopted for automobile work and for road traffic generally depends principally on the prospects of inventing a form of cylinder—or its equivalent—which will enable the driver to couple up fresh effective working parts of his machinery at will, just as may be done with storage batteries. A new form of steam cylinder designed to provide for this need will outwardly resemble a long pipe—one being fixed on each lower side of the vehicle—but inwardly it will be divided into compartments each of which will have its own separate piston. Practically there will thus be a series of cylinders having one piston-rod running through them all, but each having its own piston.
Normally, this machine will run with an admission of steam to only one or two of the cylinders; but when extra work has to be done the other cylinders will be called into requisition by the opening of the steam valvesleading to them. Provision can be made for the automatic working of this adjustment by the introduction of a spring upon the piston-rod, so arranged that, as soon as the resistance reaches a certain point, a lever is actuated which opens the valves to admit steam to the reserve cylinders of the engine. On such occasions, of course, the consumption of steam must necessarily be greatly increased; but on the other hand the automatic system of the admission to each cylinder also results in a shutting off of the steam when little or no work is required. In fact, with a fully automatic action, regulating the consumption of steam exactly according to the amount of force necessary to drive the automobile, it would be possible to work even a single cylinder to much greater advantage than is done by the machines generally in use.
So heavy are the storage batteries needed for electric traction of the road motor-car that practically it is not found convenient to carry enough of cells to last for more than a twenty-mile run. The batteries must then either be replaced, or a delay of some three hours must occur while they are being recharged. The idea of establishing charging stations at almost every conceivable terminus of a run is quite chimerical; and, even if hundreds of suchstations were provided for the convenience of the users of electric traction, the limitation imposed by being forced to follow the established routes would always give to the non-electric motor an advantage over its competitor.
The best hope for the storage battery on the automobile rests upon its convenience as a repository of reserve power in conjunction with such a prime motor as the steam-engine. A turbine worked by a jet of steam, as already described, and moving in a magnetic field to generate electricity for storage in a few cells, is a convenient form in which steam and electricity can be yoked together in order to secure a power of just the type suitable for driving an automobile. In the machine indicated the supply of the motive power is direct from the storage batteries, which can be coupled up in any required number according to the exigencies of the road. Automatic gear may be introduced by an adaptation of the principle already referred to.
In a light road-motor for carrying one or two persons on holiday trips or business rounds, the quality of adaptability of the source of power to the sudden demands due to differences of level in the road is not so absolutely essential as it is in traction engines designed for the transport of goods over ordinaryroads. In the former class of work the waste of power involved in employing a motor of strength sufficient to climb hills—although the bulk of the distance to be travelled is along level roads—may not be at all so serious as to overbalance the many and manifest advantages of the automobile principle. At the same time, as has already been indicated, there is no doubt whatever that when proper automatic shut-off contrivances have been applied for economising mechanical energy in the passenger road-motor, an immense impetus will be given to its advancement.
In the road traction-engine the need for what may be termedefforton the part of the mechanism is much greater, more especially as the competition against horse-traction is conducted on terms so much more nearly level. A team of strong draught-horses driven by one man on a well-loaded waggon is a far more economical installation of power than a two-horse buggy carrying one or two passengers.
The asphalt and macadamised tracks which are now being laid down along the sides of roads for the convenience of cyclists, are the significant forerunners of an improvement destined to produce a revolution in road traffic during the twentieth century. When automobileshave become very much more numerous, and local authorities find that the settlement of wealthy or comparatively well-to-do families in their neighbourhoods may depend very largely upon the question whether light road-motor traffic may be conveniently conducted to and from the nearest city, an immense impetus will be administered to the reasonable efforts made for catering for the demand for tracks for the accommodation of automobiles, both private and public.
The tyranny of the railway station will then be to a large extent mitigated, and suburban or country residents will no longer be practically compelled to crowd up close to each station on their lines of railroad. Under existing conditions many of those who travel fifteen or twenty miles to business every day live just as close to one another, and with nearly as marked a lack of space for lawn and garden, as if they lived within the city. The bunchy nature of settlement promoted by railways must have excited the notice of any intelligent observer during the past twenty or thirty years—that is to say since the suburban railroad began to take its place as an important factor in determining the locating of population.
To a very large extent the automobile will be rather a feeder to the railway than a rivalto it; and all sorts of by-roads and country lanes will be improved and adapted so as to admit of residents running into their stations by their own motor-cars and then completing their journeys by rail. But when this point has been reached, and when fairly smooth tracks adapted for automobile and cycling traffic have been laid down all over the country, a very interesting question will crop up having reference to the practicability of converting these tracks into highways combining the capabilities both of roads and of railways.
In an ordinary railroad the functions of the iron or steel rails are twofold, first to carry the weight of the load, and second to guide the engine, carriage or truck in the right direction. Now the latter purpose—in the case of a rail-track never used for high speeds, especially in going round curves—might be served by the adoption of a very much lighter weight of rail, if only the carrying of the load could be otherwise provided for. In fact, if pneumatic-tyre wheels, running on a fairly smooth asphalt track, were employed to bear the weight of a vehicle, there would then be no need for more than one guide-rail, which might readily be fixed in the middle of the track; but this should preferably be made to resemble the rail of a tram rather than that of a railroad.
"Every man his own engine-driver" will be a rule which will undoubtedly require some little social and mechanical adjustment to carry out within the limits of the public safety. But the automobile, even in its existing form, makes the task of completing this adjustment practically a certainty of the near future; and as soon as it is seen that motor tracks with guide lines render traffic safer than it is on ordinary roads, the main objections to the innovation will be rapidly overcome. The rule of the road for such guide-line tracks will probably be based very closely on that which at present exists for ordinary thoroughfares. On those roads where two tracks have been laid down each motor will be required to keep to the left, and when a traveller coming up behind is impatient at the slow rate of speed adopted by his precursor he will be compelled to make the necessary détour himself, passing into the middle of the thoroughfare and there outstripping the party in front, without the assistance of the guide-rail, and rejoining the track.
To execute this movement, of course, the motor wheels for the guide-tracks must be mounted on entirely different principles from those adapted for railroad traffic. The broad and soft tyred wheels which bear upon theasphalt track will be entrusted with the duty of carrying the machine without extraneous aid; but there will be two extra wheels, one in front and one at the rear, capable of being lifted at any time by means of a lever controlled by the driver. These guiding wheels will fit into the groove of the tram line in the centre, being made of a shape suitable for enabling the driver to pick up the groove quickly whenever he pleases. The carrying wheels of the vehicle in this system are enabled to pass over the guide-rail readily, because the latter does not stand up from the track like the line in a railroad.
A simpler plan, particularly adapted for roads which are to have only a single guide-rail, is to place the rail at the off-side of the track, and to raise it a few inches from the ground. The wheels for the rail are attached to arms which can be raised and lifted off the rail by the driver operating a lever. Guiding irons, forming an inverted Y, are placed below the bearings of the wheels to facilitate the picking up of the rail, their effect being that, if the driver places his vehicle in approximately the position for engaging the side wheels with the rail and then goes slowly ahead, he will very quickly be drawn into the correct alignment. Of course the rails for this kind oftrack can be very light and inexpensive in comparison with those required for railroads on which the whole weight of each vehicle, as well as the lateral strain caused by its guidance, must fall upon the rail itself.