# Popular Science Monthly/Volume 15/July 1879/Wasted Forces

THE

POPULAR SCIENCE

MONTHLY.

JULY, 1879.

 WASTED FORCES[1]
By WILLIAM H. WAHL, Ph. D.

THOSE inventions are deserving of special honor, and generally receive the most substantial recognition, which develop new industries or utilize waste products.

The glycerine industry, which has attained colossal proportions, is a notable illustration of a great manufacture based entirely upon the saving of what until lately was a waste product of the soap-boiler. As even more important, I may mention the industries connected with the manufacture of aniline dyes and artificial madder from the refuse coal-tar that was formerly the curse and nuisance of the gas-works. Old boots and shoes and leather waste are turned to good account by the chemical manufacturer in producing the cyanides, ferro and ferrid cyanides, so indispensable in color-printing and photography. Of the carcasses of slaughtered animals, not a scrap or morsel is allowed to go to waste, as you are well aware; and even the waste blood of the abattoir is used by the sugar-refiner and the manufacturer of albumen. Sawdust mixed with blood, or some other agglutinative substance, and compressed by powerful pressure in heated dies, is formed into door-knobs, hardware and furniture trimmings, buttons, and a thousand useful and decorative articles; or, as is the case with the spent bark of the tanneries, it is utilized for fuel under steam-boilers. Oyster-shells, of which our barbarous progenitors of ages ago made the shell-mounds that delight the soul of the anthropologist of to-day, are burned to lime; the waste of the linseed-oil manufacturers is eagerly sought after as food for cattle; the waste ashes of wood-fires are leached for potash; river-mud is mingled with chalk, and burned and ground to make the famous Portland cement; and the ruthless hand of Utilitarianism has not even respected the brickbat, that had served from time immemorial only to crack the heads of opposing factions, but grinds it up to make cement with lime. The finest glue size is made from the waste of parchment skins. The waste gases of the blast-furnace are now utilized to heat the blast, to generate the steam that drives the engine that makes the blast, to hoist ores, drive machinery, etc.; and even the slag, that has served for years only to decorate the hillsides, is now cast into paving and building blocks, or granulated to make building sand, or ground for cement, or mixed with suitable chemicals and turned into the commoner grades of glass, or blown by a jet of steam into the finest filaments to form the curious substance called mineral wool, now largely used as a non-conductor of heat upon steam-pipes, boilers, roofs, etc., etc.

So, too, the enormous hills of anthracite-coal dirt, that in the coal regions of our State have for years borne silent but eloquent testimony to the crudity and wastefulness of our methods of mining coal, now bid fair soon to disappear beneath boilers supplied with ingenious dust-burning devices, or in the form of lumps of artificial fuel. Even the anthracite-coal deposits, now so enormously valuable, were a few years ago but so many layers of black stone, unappreciated and valueless. The waste heat of the lime-kiln is made to generate steam, and warm immense public buildings in England and on the Continent; and the “exhaust” of the steam-engine is made to do service in heating the water fed into the boiler.

I might multiply examples like the above almost indefinitely, to show how, with the most beneficent results, the genius of invention has enabled us to reap advantages where none were supposed to exist, or where, if they were suspected, they were undervalued or simply neglected.

And now, having briefly shown, by a few typical examples, what modern invention has done and is doing to utilize the waste products of nature and of the arts, I shall invite you to consider with me whether there are not waste forces in nature that can and should be turned to useful account, or to vastly better account than we are now putting them; and whether we must not plead guilty to the crime of neglecting to avail ourselves of exhaustless and incalculable stores of power that simply wait to do our bidding.

Before I pass to the consideration of what I have called the “Waste Forces of Nature”—by which I mean to designate such of the natural powers as the world of industry has thus far passed over altogether—it will be instructive for us to consider whether we are doing what we ought to do with those that are used, and whether, with all the inventions of our skilled mechanics and engineers, the actual practical results that we obtain from the various sources of power used in the industries do not fall far below what theory declares it to be possible to attain. Suppose we take steam, the almost universal motive power of to-day, as an example, and put the inquiries, What ought we to get out of it and what do we get out of it? And when I am through, I think that many of my hearers, who have heretofore entertained the belief that steam-engineering was a field that had been so thoroughly worked up that but little remained to be accomplished in the direction of increasing the duty of our steam-motors, will be willing to acknowledge themselves mistaken.

To get at the practical duty of a steam-engine, we must begin with the source of the power, the steam-generator—popularly and most inappropriately called the steam-boiler; and, as the source and origin of the power generated in the boiler and directly traceable to the combustion of the fuel, it is evident that we must begin with that. Let us inquire, therefore, what power we ought to get from a perfect steam-engine burning pure coal, and then compare it with what we do get in the best steam-engine practice of to-day.

To understand the deductions I shall shortly make in getting at this comparison between theory and practice, I prefer to invite you to follow me through a few theoretical considerations, rather than ask you to accept the conclusions simply on my bare assertion.

It has long been known that a definite relation exists between the quantity of heat developed in a given operation and the quantity of mechanical force (manifested as work) that could be obtained from that heat. The absolute nature of this equivalency is tacitly recognized, though perhaps imperfectly comprehended in the practice of every branch of industry employing heat as a source of power; for it is this fact which establishes the dimensions of the steam-boiler, and the several proportions of the engine to do the work required of it. The steam-engine, in simple language, is simply an apparatus for turning heat into work; and it is, therefore, quite possible to express the value of a given quantity of the form of energy we call heat in terms of mechanical energy that we call “work”; and scientific investigation has established an admirable unit for this comparison in the “foot-pound”—that is, the force required to raise a pound weight to the height of one foot.

Now, to estimate the value of heat in terms of work, it was found necessary to determine the amount of mechanical force necessary to raise the sensible heat of one pound of water one degree in temperature. This amount has been carefully determined by several eminent savants, and has been given the name of the “mechanical equivalent of heat.” The value of this constant has been found to be 772 foot-pounds that is to say, the mechanical energy possessed by a body weighing one pound, after falling from a height of 772 feet, would, if it could all be converted into the form of energy we call heat, be exactly sufficient to raise the temperature of one pound of water 1° Fahr. (where the centigrade thermometer is employed, this constant will have a value of 772 × 1.8 ${\displaystyle =}$ 1,390 foot-pounds). Now, this much having been gained in fixing the principle of our calculations, let us go back to our steam-boiler, and to the coal we feed it with. It has been experimentally determined that, if the entire quantity of heat given off during the burning of one pound of pure coal could be applied without loss to heating water, it would suffice to raise the temperature of one pound of water 7,900° C.; or, what is the same thing, differently stated, it would be sufficient to raise the temperature of 7,900 pounds of water one degree. The possible mechanical duty of the “theoretically perfect” steam-engine is found by simply multiplying the quantity which expresses the thermal equivalent of coal by the quantity which expresses the mechanical equivalent of heat, and the result would be the true value of one pound of coal burned in the boiler in “foot-pounds.” Performing this simple arithmetical operation, we obtain (7,900 × 1,390 =) 10,980,000 foot-pounds; or, to put it more simply, suppose we convert these foot-pounds into horse-power, which we can do by another simple arithmetical operation of dividing them by 33,000, and we shall have as a result that one pound of pure coal, burned in the perfect boiler in one minute, would, if we could apply it with absolute economy to the performance of work, exert a force of (1098000033000 =) 332 horse-power during one minute; or, if burned during an hour, then one sixtieth of 332, or 5.5 horse-power.

With a perfect boiler, therefore, we ought to get 5.5 horse-power per hour out of every pound of coal burned on the grate-bars. Now, let us inquire, What do we get in practice? Surely, you will say, our scientific mechanics and engineers have succeeded in getting a goodly percentage out of this possible figure; and the splendid engines, of massive construction, that work so beautifully as to excite our wonder and admiration at their smoothness and ease of their movements, must be very near perfection. Alas for the vanity of human expectations! Instead of getting 5.5 horse-power out of every pound of coal we burn in the boiler, the very best boiler and engine that have ever been constructed require two and a half pounds of coal to give out one horse-power: which means that, in spite of the vaunted progress of the mechanic arts in our times, the best engineering talent applied to the improvement of the steam-engine, from the time of James Watt down to Corliss, has only succeeded in making it yield a duty of 15 per cent. of what it ought to do, leaving an enormous margin of 85 per cent. for future improvements.

In the foregoing remarks I have, I fear, inadvertently been unjust to our engine-builders, for by far the greater portion of this 85 per cent. of wasted power is chargeable directly to the steam-boiler, and but a comparatively small proportion thereof to the engine. In considering the question of the duty of steam-motors, however, we must take the whole machine (engine and boiler), as a single apparatus. If our boiler-makers could do as well as our engine-builders—the two industries are quite separate, as you may know—the showing would he much more favorable.

It will be instructive, I think, to trace out the causes of the great waste of power that I have just pointed out, and to see if there are no means of remedying them. And if you will follow me, they will be very apparent.

The first and greatest source of loss resides in the difficulty—I may, I think, safely say the impossibility—of burning solid fuel economically in any form of furnace that has yet been devised; and this prime difficulty is an unanswerable argument in favor of the substitution of liquid or gaseous fuel for steam-making as for other purposes. Let us analyze the matter: The buyer of coal purchases at the outset at least 10 to 15 per cent. of non-combustible and useless material with every pound of coal, in the form of ash; while at least 5 per cent. more of the coal is lost by falling through the grate-bars in the form of the dust or partially burned fragments that find their way into the ash-pit unutilized. If even now, with so much waste as I have just indicated, we could really turn to useful account the whole of the thermal effect of the 85 per cent, or 80 per cent, of the combustible that we have left, we might well be content; but such is far from being the case. The furnace gases can not, by any possible mode of constructing boilers, be retained long enough in contact with the steam-generator to yield up all their heat, and they are thrown out from the chimney frequently at a temperature of 800° Fahr.; and, what is still worse, their combustion is frequently so imperfect that they carry off with them out of the chimney great volumes of unburned carbon in the form of smoke; the cold air with which the fuel is fed, and which must become highly heated before it will begin to combine with the fuel, and which abstracts this heat from the glowing coals through which it passes, is another serious item of loss, which is intensified by the necessity of frequently opening the furnace-doors when large volumes of cold air rush into the fire-space; and, lastly, the conduction and radiation of heat from the generator to surrounding objects complete the category of losses. Summing up all the items of loss in the steam-generator, it is probable that with the best forms of boilers which it has been possible to construct, not more than 25 per cent. of the theoretical thermal effect of the fuel is utilized in the generation of steam; and of this 25 per cent., from 5 to 10 per cent, is lost somewhere on the passage of the steam from the boiler to and through the engine by condensation in steam-pipes, and friction of the machinery, leaving us but 15 or 20 per cent, actually realized in practice. I beg that you will not think that I have purposely made the case of the steam-engine worse than it is; for, so far from doing so, I have actually made out the most favorable possible showing for it, by selecting for my example the best practice of the best makers.

Much of this loss, possibly the half of it, I have no hesitation in ascribing to the use of solid fuel—coal or wood. And I take this opportunity of putting myself on record before you, as I have done for years persistently in the scientific journals, as an earnest advocate of fuel in the gaseous form, not only for industrial and manufacturing purposes, but also in the household. Let me give you a few thoughts on this subject.

The great and obvious advantage of gaseous fuel—to leave the question of its convenience, at present, out of sight—resides in the fact that the character of the fuel permits of its instantaneous and perfect intermixture with the air, by which a vastly more perfect combustion is insured—an advantage that finds admirable expression in the regenerative furnace of Siemens. Where Nature, however, supplies us with an abundance of combustible gases, as in certain favored localities in our oil regions, to which I shall have occasion to refer hereafter, an additional advantage is gained, since she has saved us the necessity of making it; and the practical utilization of the product of the numerous gas-wells of our oil regions has proved of enormous advantage to the manufacturers of these localities.

But in addition to the advantage I have just alluded to, namely, the great gain due to the more perfect combustion of gaseous fuel, there are other advantages on the score of convenience and economy that are no less important. I refer here to the saving in the carriage of coal from the yard to the place of delivery, and the recarriage of ashes—charges which are especially onerous in the numerous cases where boilers, stoves, etc., are located in the upper stories of buildings, or situated inconveniently as regards ordinary delivery by wagons. The saving in wages of stokers, to clear the fireplaces, and keep the heat of the furnace always at the proper intensity—difficulties which the adoption of gaseous fuel would entirely obviate, since it furnishes no ashes to remove—and the proper regulation of the gas supply, would insure a perfectly uniform heating effect for hours together, without supervision or attention of any kind. The incidental saving of fuel or steam, whenever, by improper regulation, or the inattention of stokers, the furnaces are allowed to become too hot; and, on the other hand, the saving in time and material that would otherwise be wasted by low fires and the frequent necessity of stoppages, until the required steam pressure is restored; and last, but not least, the great saving of fuel now universally wasted in keeping up boiler, and range, and heater, and stove fires overnight, and at all seasons—all these, and other items that I have probably overlooked in this hasty outline of the subject, form together an array of objectionable features sufficient to bring any system into disuse, where a remedy so easy to apply as the adoption of fuel in the gaseous state is at hand.

I do not wish to be understood as intimating that the use of our common burning-gas would be a panacea for all the ills I have narrated, for its cost would preclude its general adoption for industrial purposes, to take the place of coal or wood. For domestic purposes, however, in the form of gas-stoves, even at the present high cost of this form of gas, it has been already largely adopted, and with advantage and economy; while for every form of light work, where power is only required intermittently, as in printing-offices, elevators, hoists, and the like, gas-engines, using ordinary coal-gas, are, even at present prices, decidedly more economical than steam, since they may be started and stopped instantaneously, and when idle are wasting nothing. And in the case of a steam-engine the steam must be kept up all the time, though the engine may not be wanted more than an hour or two in the day.

I look forward to the time, and I believe it is not far distant, when we shall have “heating-gas” laid through the streets of our cities and towns, side by side with lighting-gas and water-mains, and when our mills, and factories, and workshops, our parlors and kitchens, will be supplied with heat from that source, and when fires of wood and coal, with their abominations of dirt and ashes, and extravagance, will be looked upon as nuisances of the “good old times” when they knew no better.

To come back again to the subject of the steam-engine, from which I have digressed further than I had intended, I may mention the circumstance that the enormous wastefulness of this species of motor has originated the thought that electrical engines might be constructed to develop power more economically. A consideration of this topic, however, would take so much of our time this evening that I must pass it by with the brief remark that the galvanic battery can not compete in economy with the steam-engine, until some cheap mode of generating electricity shall be discovered. The fuel of the battery is zinc, and, even though we can get fifty per cent. of its theoretical power by burning it in the battery, its cost is so much higher than that of coal, the fuel of the steam-engine, that the latter has the advantage, at the present time, of forty to one on its side.

The recent great advances, however, that have been made in the construction and improvement of what are known as dynamo-electric machines, by which mechanical power, no matter how generated, whether from the steam-engine, the wind, or waterfall, could be directly converted into electricity, appear to have solved the problem of the cheap generation of electricity in any quantity, and have opened a wide field of speculation as to the possible extensive introduction of magnetic engines to take the place of steam. For I need scarcely tell you that electricity can be transmitted with but very little loss over great distances, by metallic conductors properly insulated, and made to drive magnetic engines to do the work of steam, or to furnish light for cities and towns, at pleasure. I shall take occasion to revert again to this very interesting topic in the course of the evening.

This remark brings us at length directly to the theme of my discourse—the “Waste Forces of Nature,” to which I now invite your attention.

Of these, the first to be named, from the magnitude of the possibilities that advanced thinkers have attached to it, is that fountain of all terrestrial energy, our sun.

To introduce this topic properly, I beg to remind you at the outset that the progress of science during the last half century has been most pronounced and satisfactory in the investigation of the nature, origin, interdependence, and interconvertibility of the various manifestations of energy that are called familiarly “the forces of nature”; and among the most philosophical generalizations that the science of our times may boast of having established is the demonstration, upon the most complete and satisfactory experimental evidence, that every manifestation of terrestrial activity has more or less directly a solar origin. Every exhibition of force, physical or chemical, inorganic or vital, the multifarious consequences connected with the circulation of air and water over the surface of the earth, and in her oceans, and which involve the causation of the winds, aerial and aqueous currents, and rainfall, and the effects of these commonplace but vastly important phenomena in establishing and maintaining those climatic conditions upon which the existence of life upon the earth is absolutely dependent, are directly referable to the forces of solar radiation. Ay, there is good reason for the belief, which is entertained by most competent and eminent authorities, that the periodical recurrence of famines and pestilences and other scourges that afflict mankind, and which the superstitious of all ages are wont to ascribe to the anger of an offended deity, coincides with the periodical maxima and minima in the intensity of the solar emanations that reach the earth; and that even such apparently disconnected and arbitrary things as the social and political affairs of mankind, which are intimately bound up with the successful pursuit of agriculture and commerce, are therefore demonstrably under the direct and immediate dominion of the solar rays.

But, to return from a digression that is only of incidental interest to us here, I desire you to conceive of the amazing fact that the stupendous aggregate of terrestrial activity is derived from that infinitesimal fraction only of the solar emanations that is intercepted by the earth—a fraction less than the two-billionth part of the sum total of energy that he is unceasingly radiating into space; and it is my immediate purpose here to invite your attention to the interesting question whether it is within human reach to convert a portion of the measureless floods of power that the sun pours out upon the earth into mechanical energy, or into other forms in which it will be more directly available for useful purposes.

The proposition here announced, I must advise you, is not the visionary notion of impracticable theorists, but is one that, on the contrary, has seriously occupied the attention of such eminent practical engineers and mechanics as Ericsson, and others scarcely less widely and favorably known; and, although up to the present time nothing very tangible has resulted from their labors, they have at least succeeded in demonstrating, beyond reasonable doubt, that the problem is susceptible of practical solution.

To convey some adequate notion of the incalculable floods of power that await the bidding of the compelling genius of invention, I will invite your attention to a very brief résumé of the well-substantiated results of scientific research applied to the subject. The French physicist Pouillet, with the aid of elaborately refined apparatus, estimated that the earth receives from the sun in each and every minute 2,247 billions of units of heat—a quantity sufficient, if converted into mechanical force, to raise 2,247 billions × 774 pounds to the height of one foot. To come down to figures that are less difficult of conception, let us confine our attention to that part of the solar heat that falls upon the oceans, and to the fraction of that portion which is expended in the work of evaporating the water.

Without entering into an explanation of the modes in which the following calculations have been made, and which would run into far greater length than the limited time at my disposal this evening would warrant, I will simply give you the results.

I have said, you will remember, that we would confine our attention to that portion of the solar heat that falls upon the oceans, and to that fraction of it which is expended in the work of evaporating the water; in doing which alone, the sun raises during every minute an average of not less than 2,000,000,000 tons of water to a height of 312 miles—the mean altitude of the clouds. To express this prodigious exercise of power in more familiar form, I may put it this way, that to continuously raise this weight of water to the height of 312 miles per minute would require the continuous exercise of the force of 2,757,000,000,000 horses per minute.

Here, then, is power enough to satisfy the most enthusiastic inventor, and leave him plenty of margin; and if the believers in the sun-engine shall ever succeed in giving mechanical expression to but the merest fraction of this superabundance, they may safely count upon creating as profound a revolution in the world of industry as that which was ushered in with the steam-engine.

Ericsson, who has devoted much study to this enticing problem, has announced his unqualified belief that the sun-engine is practicable. He has progressed so far as to lay down the general principles on which he proposes to construct such a motor, and which he has actually put into practice in the production of an engine that runs with great uniformity at a speed of 240 revolutions per minute, and consuming at this rate only part of the steam made by the solar generator employed. From the very brief and imperfect accounts that have been made public, it appears that the Ericsson sun-engine is composed of three distinct parts—the engine proper, that is, the working mechanism, the steam-generator, and the concentrating apparatus, by means of which last the feeble intensity of the sun's rays is augmented to the degree that will suffice to produce steam at a practical working pressure.

He claims that this concentrating apparatus will abstract on the average, for all latitudes between 45° north and 45° south, fully 312 heat-units for every square foot presented vertically to the sun's rays. With 100 square feet of surface in his concentrating apparatus, therefore, he believes it will be possible to continuously develop from the sun's rays 8·2 horse-power during nine hours within the above-named range of latitude.

Mouchot, who, so far as the practical construction of the solar engine is concerned, has progressed further even than Ericsson, exhibited at the late Exposition at Paris a working sun-engine upon substantially the same general principle of construction as that above described, and which, from its novelty and the importance of the principle it illustrated, received universal popular attention and a most encouraging and flattering report of the judges of awards.

Not to over-estimate the capabilities of the new system, Ericsson, in his consideration of the practical side of the subject, assumes that a sun-engine of one horse-power will demand the concentration of heat from one hundred square feet; and on this estimate he proceeds to show that in all reasonable probability those regions of the earth that now suffer from an excess of heat will some day derive such benefits from their unlimited command of motive power as to vastly overbalance their climatic disadvantages. He proposes the sun-engine only for those regions where there is steady sunshine, and has mapped out extensive tracts of land aggregating no less than 9,000 miles in length and 1,000 miles in breadth, including therein the southern coast of the Mediterranean, Upper Egypt, much of the Red Sea region, the greater part of Persia and Arabia, and portions of China, Thibet, and Mongolia, in the Eastern Hemisphere; and Lower California, the Mexican plateau, Guatemala, and the west coast of South America for a distance of 2,000 miles, as the field of the solar empire of the future. As an evidence of the sincerity of his belief in the realization of these ideas, let me quote you the following enthusiastic passage from one of his numerous essays upon this subject: “The time will come,” asserts Ericsson, “when Europe must stop her mills and factories for want of coal. Upper Egypt then, with her never-ceasing sun-power, will invite the European manufacturer to remove his machinery and erect his mills on the firm ground along the sides of the alluvial plain of the Nile, where sufficient power can be obtained to enable him to run more spindles than a hundred Manchesters.”

For centuries past the wind has been put to work with very good results, and in some countries, notably in Holland, quite extensively. From the best advices I have upon this topic I have it that there are in that country no less than 12,000 windmills, averaging eight horse-power each, giving a total of 96,000 horse-power.

The chief and obvious difficulties that intrude themselves against the extensive use of the wind as a motive power for general industrial uses are that in most locations it is intermittent in its action, extremely variable as to its power, and quite unreliable as to the time and duration of its manifestations.

The immense power stored up in this unfortunately unreliable agent will appear from the statement that a wind of three miles per hour travels 4·40 feet per second, and exerts a pressure of 0·32 to 0·44 pound per square foot of surface opposed to its action. A wind of twenty-five miles an hour, or what sailors would call a good stiff breeze, travels 39·67 feet per second, and exerts a pressure of from 2·208 to 3·075 pounds per square foot. The prodigious energy of a hurricane, traveling not infrequently at the rate of one hundred miles per hour, is too well known by its disastrous effects to need repetition. The power of the wind, however, save for ship-propulsion, is utilized in but few situations, its unreliability having caused it to be but very slightly esteemed in comparison with water-power and steam. Of late, however, small windmills, especially designed with superior mechanical skill, have been rapidly growing in popularity in this country, mainly for pumping water for railway and domestic purposes, an application for which these devices are excellently adapted; and I entertain no doubt that there are many situations where work is to be done that does not demand a continuous exercise of power, and where the prime consideration to be observed is the element of cheapness, where wind-power might be most advantageously employed. There are, again, extensive regions of the earth, extending for ten or more degrees north and south of the equator, where the winds blow continuously from one direction throughout the greater portion of the year—I need hardly remind you that I refer to the region of the “trade-winds,” and in which, especially along the coast-line where their influence is not disturbed by mountain ranges and other conflicting causes, the force of the wind may be relied upon with almost absolute certainty for the whole or the greater portion of the year. In such regions, therefore, Nature has supplied us with an exhaustless store of energy, capable of meeting the most extravagant demands that may be made upon it. Even the region of the temperate zones, where the winds are variable, our seashores have their strong land- and sea-breezes which for nine days out of ten may be relied upon; and even in situations where wind-power is most unreliable, as in the interior of the continents, there is a vast and valuable field open for some practical and generally applicable system by which the power of the wind, at present almost universally allowed to go to waste, may be stored up to be given out again as it may be required for service; for it may be made to coil a spring, to raise heavy weights, or lift water into elevated reservoirs, or, by other simple devices well known to the mechanical engineer, to store up its power, which may be subsequently given out through machines especially adapted for the purpose.

The tides ebbing and flowing twice daily, lifting upon their bosom, like so many corks, the heaviest vessels, and baffling all efforts to restrain their resistless force, afford us another instructive topic for consideration in treating of the wasted forces of Nature—for here, again, she has lavished out of her superabundance infinitely more power than any conceivable increase of the needs and industries of man could ever employ.

The rise and fall of the tides vary, according to local conditions, from a few inches, as in the Mediterranean Sea, to seventy feet, as in the Bay of Fundy, and their force in almost any one of our rivers would, if properly applied, suffice to furnish ample power to all the mills and factories and workshops that could be built side by side upon their banks. They would drive under-shot wheels unfailingly. Where there are extensive meadows regularly overflowed, as they commonly exist along all of our larger streams, a levee containing two sluices, each supplied with a turbine water-wheel, one to be driven by the ebb and the other by the flow, could be made to utilize incalculable power.

In some exceptionally favorable localities, where the conditions have forced themselves upon the attention of observing and practical men, tide-motors have been introduced, and with great advantage; but the general utilization of these exhaustless and continuous stores of energy still remains to be accomplished.

Great rivers above tide-water are rolling down a wealth of power in their currents; and a hundred factories along their banks, heedless of the fact, are using steam-power. And it is one of the standing marvels that manufacturers fail to recognize the elementary fact in mechanics, that it is not necessary for a stream to have from ten to two hundred feet of fall, in order to do their work; while the great rivers upon whose banks their workshops are perched are permitted heedlessly to pour out trillions of cubic feet of water, year after year, into the ocean, opposing no mechanical difficulties in the way of yielding up their inexhaustible supplies of power.

Who may estimate the wealth of power poured out in unheeded profusion by our great waterfalls from Niagara down? Confining our attention to the one grand cataract, try to conceive of two million tons of water per minute hurled down that ledge of rock, representing 50,000 horse-power expended every minute in the work of disintegrating and undermining the rocky river-bed below. A few tiny paddles, I am told, dip into the current above the falls, and drive a paper-mill, but what of the millions of horse-power that are allowed to rim heedlessly to waste down that great fall of 157 feet, in a sheet twenty feet thick and 4,750 feet broad?

The gas-wells of the oil regions have been permitted to spout away wealth enough to have repaid a hundred-fold all the money ever lost in oil speculations; but it is gratifying to be able to say that the great value of these natural supplies of heat and light is now very generally recognized, and that in many localities the gas is turned to useful account in supplying light and heat to towns and cities and factories and mills.

In some of the cases that I have called to your attention, the power is steady and unremitting, in others it is too violent or too uncertain for direct application. In the first instance, uses for the power may be found at once; in the last, means for storing it up must be provided, and would, beyond question, abundantly repay the undertaking. For this purpose, the raising of weights or of water into elevated reservoirs, and the compressing of air, afford two simple and ready means of storing up power to be let loose as required; while other means of a mechanical nature to accomplish the same purpose will readily occur to my mechanical hearers.

While upon this point, I must not omit to state one fact of the greatest interest that is now attracting the attention of some of the highest living authorities. I refer to the question of the practicability of transmitting mechanical power to great distances by converting it into electricity, through the agency of what are called dynamo-electric machines, and utilizing this either for the production of powerful lights for illuminating cities and towns, or by converting it back again into mechanical power with the aid of magneto-electric engines, by which mills, factories, and workshops may be furnished with the power they now obtain from steam or water. It will be very à propos, in this connection, to notice that the feasibility of transmitting to great distances the almost incredible power of Niagara Falls, by some such means as that above named, has been affirmed by many scientific investigators of eminence.

Dr. C. W. Siemens, in his presidential address before the last meeting of the Iron and Steel Institute, in touching upon the highly interesting subject of the employment of electricity as a substitute for steam, made the following instructive statements: He declared that so long as the source of electrical power depended upon the galvanic battery, it must, in the present state of things, remain far more expensive than steam-power, for the obvious reason that zinc, which is the fuel of the galvanic battery, is vastly more expensive than coal, the fuel of the steam-boiler. If, however, continues Dr. Siemens, a natural force, such as water-power, mark you, could be utilized to generate electricity economically, the case would be very different. A dynamo-electric machine actuated by water-power could be made to generate powerful electrical currents, which could be transmitted through insulated metallic wires or cables to a great distance with but little loss, comparatively speaking, and could thus be made to run magneto-electric engines to do the work of steam in our mills and workshops, to ignite electric lamps, etc. A copper rod, or cable, three inches in diameter, says Dr. Siemens, would be capable of transmitting a thousand horse-power to a distance of say thirty miles—an amount sufficient to give the light of a quarter million of candles, and suffice to illuminate a town of moderate size. Two eminent American investigators, Professors Houston and Thomson, of Philadelphia, having just made an investigation with the especial purpose of determining the practicability of transmitting the power of Niagara to great distances by means of electricity, go even further than Dr. Siemens. They make the astonishing assertion—and, what is more, they prove it—that it would be possible, should it prove to be desirable, to convey the whole power of Niagara to the distance of 500 miles or more by means of a copper cable not exceeding a half inch in thickness.

It is unnecessary for me to multiply examples upon this fruitful theme of speculation, for the time admonishes me that I have already trespassed sufficiently upon your attention, and I think I have convinced you very fully that such queries as What shall we do when our coal-fields are exhausted? need cause us no anxiety, for centuries before this possibility shall be realized, I opine, the world will no longer stand in need of them.

1. An address delivered at the opening of the spring course of lectures of the Wagner Free Institute of Science, Philadelphia, March 1, 1879.