energy possessed by the elastic force of the spring of the piece of clockwork is exactly equivalent to the amount of energy expended or work done by yourself in winding it up, and the work which it is capable of doing is exactly equal to the work done by you. No energy has been created or destroyed-it has only changed its form. Yes! some one will say, perhaps, "this is no doubt true, but when your stone has fallen to the ground and come to rest, or when your piece of clockwork has performed its little evolutions, how about your energy' then?" I reply, "its energy has not been destroyed, it has been converted into heat, just as the energy of a railway train is converted into heat when it is suddenly stopped (as the sparks from the surface contact of the wheels and brakes testify), or the energy of the bammer after it has struck the anvil or the cannon-ball, the target. There has been, in a word, an annihilation of so much visible energy, simultaneous with the creation of so much heat." But, you say, 66 Do you mean to assert that no energy is created in the case of the steam-engine, the electric dynamo, the muscular exertions of men and animals, the windmill Surely these all create force? The pulley, the lever, the hydraulic press, the wheel and axle. What are these for but the creation, the production of force?" "No! by neither steam-engine, electric dynamo, human muscle, nor any mechanical contrivance is any force created."

Let us take a simple case first-that of the pulley. Take a system of pulleys in daily use by mechanics and others, consisting of two blocks, the lower one of which is movable, and the upper one is fixed. There are three pulleys to each block, and the same string goes round all the pulleys. On the end of the string, passing over the upper block, is hung a weight of one pound; from the lower block is suspended one of six pounds. The system is in equilibrium in any position of the weights. One pound therefore balances a weight of six pounds, and by exerting a certain force at the end of the string passing over the upper block, I am able to raise a weight six times as great-neglecting friction. Observe, how ever, that I have to move my end of the string through a much greater space than that through which the weight ascends, and if you measured these two distances,

you would find that to raise the weight of six pounds ONE foot you would have to remove the end of the string passing over the upper block through six feet, or a space six times as great.

What we gain in power we lose therefore in space. Similarly, if you have four pulleys at the lower and upper block.e., eight in all-you would then have eight strings passing around the lower block, then with a force of a little more than one pound, you would be able to raise a weight of eight pounds, but you would have to move your string through a space eight times as great as that through which the weight ascended. And so on for any number of pulleys, but always the saine law holding, that what we gain in power we lose in space.

There is no creation of energy, but simply a transformation of one kind into another more convenient to us, and similarly in all machines or combinations of machines this law is universally true, that "what we gain in power we lose in space,' or that the power multiplied into the distance it descends is always equal to the weight multiplied into the distance through which it ascends - neglecting friction.

Let us turn now to the case of the steamengine. First of all, however, let me point out that the various forces of Nature, such as gravity, heat, light, electricity, magnetism, chemical action, etc., are so related that any one can be made to produce the other, directly or indirectly. For example, a stream of water flowing from a higher to a lower level, under the action of gravity, may be made to turn a water-wheel, which sets in motion a Gramme machine. This motion is converted into heat and electricity; this electricity produces the electric light, and light, we know, causes chemical action (i.e., oxidation in the animal system), which supplies muscular power, which may set in motion a Gramme machine, whose motion may again be converted into heat, electricity, and so on, indefinitely. In the case of the steam-engine, this machine converts heat into mechanical force, which drives the engine, just as, vice versa, mechanical action gives rise to heat; as, for instance, the mechanical movements of various wheels, axles, pistons, etc., of the steam-engine, sometimes make thein so hot, that accidents happen by these means.

Now and here is the whole secret of the matter: The steam engine converts the heat into an exact mechanical equivalent of the heat produced, a certain amount of heat always producing a certain amount of mechanical action, and a certain amount of mechanical action, a certain amount of heat, neither more nor less.

It is chiefly to the labors of Mr. James Prescott Joule (of Manchester) that we owe the transforming of these doctrines from the field of speculation and their placing upon the sure basis of experimental fact. The greater part of his elaborate and exhaustive experiments and researches consisted in his ascertaining what quantity of heat would be produced by a given quantity of work.

A certain known weight was attached to a pulley having its axle resting upon friction wheels, to diminish, as much as possible, the friction caused by its revolution. A string passing round the pulley is wrapped round a vertical axle inserted into a round, vertical, covered vessel, which axle was caused to rotate by the downward motion of its weight. Now to this vertical axle was attached a system of paddles, which moved with the axle. There were, altogether, eight sets of these paddles revolving between four stationary vanes. When, therefore, the box was full of liquid, the paddles and the vanes together churned it about, the stationary ones preventing the liquid being carried round with the paddles. The heat generated in the liquid, when the weight fell through a certain distance, was accurately measured by a thermometer, and he thus deduced that the fall of a weight weighing one pound through a vertical distance of 772 feet, raised the temperature of one pound of water from 32° to 33° Fahrenheit.*

This number 772 is called the mechanical equivalent of heat, and is a constant of the greatest importance in scientific and practical observations.

Now, in the example of the steam-engine already alluded to, we have heat-producing mechanical action, or work-the opposite of Joule's experiment. The quantity and temperature of the steam entering the cylinder of the engine may

* Or in the more correct scientific phraseol

ogy of the day, 424 kilogrammetres one degree Centigrade. When will English conservatism allow the universal adoption in this country of the much simpler French metrical system?

be measured, and from these the amount of heat passing into the cylinder-per minute, say-can be calculated. In the ordinary steam-engine a large portion of the heat is, of course, yielded to the condensing of water, and another part is lost by conduction and radiation from the cylinder, pipes, condensers, etc. All these quantities may, however, be estimated and allowed for, and when the result is compared with the quantity of heat entering the cylinder a difference is found which leaves a quantity unaccounted for; but when the quantity is compared with the work done by the engine in the same interval, it is always found that for every 772 units of work, one unit of heat has disappeared.

Tested, as this may be, within the limit of experimental error, the result is always the same. Equally definite quantitative relations are found to exist between all the other forms of energy. To produce a certain amount of one kind of energy, the equivalent amount of another kind of energy is always necessary, and we are led to this great truth: "that the total energy of any material system is a quantity which can neither be increased nor diminished by any actions between the parts of the system, though it may be transformed into any of the forms of which energy is susceptible" (Clerk Maxwell). No scientific truth stands upon a firmer basis than this principle--known as the "Conservation of Energy"-for toward no other principle has so much ingenuity on the part of man, from times immemorial, been so fruitlessly directed.

We have all heard of "Perpetual Motion." Some of us may have known "Perpetual Motionists," whose search was not (as some suppose) for continuous motion, but for a machine that could do useful work without the expenditure of any power upon it. A pump that would continually pump water without having any force of any kind applied to any part of it, or an engine that would go without any fuel of any kind, would be a machine like that which they were seeking to make.

Now this principle of the "Conservation of Energy" simply states that, no matter what agents may be called into play, nor how much ingenuity expended on the part of man, "perpetual motion," or the creation of force, is impossible. When energy passes from higher or more

available to a lower or less available form it is said to be degraded. For instance, a piece of wound-up clockwork possesses, in virtue of its being wound up" potential or position energy" the power-supposing it was connected with some other piece of apparatus-of doing useful work. Allow it to expend this energy, which becomes converted or degraded into heat degraded because, although the amount of heat given out by it while running down would, if I could collect it, do just the same amount of work that the machine accomplished in running down, it is, of course, impossible for this to be done. All the different forms of energy can be directly or indirectly transformed into heat. A given quantity of heat-energy cannot, however, be wholly transformed into one of the higher or more available forms of energy. Just as from a level sheet of water you can gain no mechanical effect except from the flow of water from a higher to a lower level, so likewise, in the case of a heat or steam-engine, you must have a fall of heat from a body of a higher to one of a lower degree of temperature. Place a glass piston containing a small quantity of water in the flame of a spirit lamp-the increased temperature of the water inside causes an increase of pressure upon the cylinder and the piston is driven out; then blow upon it-it becomes cool, condenses the steam inside, diminishes its pressure, and the pressure of the atmosphere drives the piston in again.

In this little experiment you have the steam-engine in miniature, only in many engines instead of condensing the steam it is allowed to escape into the air and the piston is forced back by steam entering at the other end of the cylinder. In every instance, however, useful work is alone done owing to the difference of pressure and, therefore, of temperature between the different parts of the engine, or between the engine and the outside air. Where the temperature and therefore the pressure outside the boiler or piston is the same as that inside, no work could, of course, be done. Clausius, Rankine, Thompson, and others have carefully studied the laws of this change, and from their researches we learn that (theoretically), supposing the temperature of the steamengine to be 120 Centigrade and that of the condenser or outside air 20° Centi

grade, the proportion of heat used would be one-fifth. Practically, however, it will not be anything like so large as this. Thus you see what a very imperfect energy-converting machine a steam engine is. All chemical combination causes manifestation of heat, and every where that we know of throughout Nature this great conversion or degradation (owing to heat being a lower available form of energy) of energy is going on.

Our sun, like every other sun, planet, and satellite, is radiating its energy into space, tending to make the temperature of its mass uniform, and the same as that of the luminiferous ether through which it travels. All movement in this universe necessitates the expenditure of force, and therefore of work. Movement or motion (in one sense) is the cause of everything, and so we can neither do nor obtain anything without a certain expenditure of work-a certain transforming of potential. or position energy into kinetic or actual energy, or vice versa.

66

"Work is worship," says an old prov. erb. "Work is a necessity," is the doctrine of modern science. For a certain amount of one kind of energy, I will give you," says Nature," so much of the other kind of energy, neither more nor less." There is no cheating Nature. She may be a hard taskmaster, yet she rules us with strict justice. Our whole life consists but in the transformation of these two different kinds of energy. procure food (kinetic energy) which we eat, the greater part of which, under the chemical action (i.e, potential energy)* of the various juices of the digestive organs is absorbed into our system, which thereby enables us to perform a certain amount of work, mental or physical. In other words, to transform a certain amount of potential into kinetic or actual energy.

We

For a certain amount of work to be done (without waste or injury to our system) a certain quantity of food must be absorbed, i.e., digested. (Hence the value of a

"In the present state of science, chemists figure to themselves chemical action as a rearrangement of particles under the action of forces tending to produce this change of arrangement. From this point of view, therefore, chemical agency' is potential energy."

-CLERK MAXWELL.

It is, of course, often very difficult to deter

mine, in some cases, which of the two forms of energy it is. ONE of the two it must be.

upon the land which these unsightly things would cover.

good digestion.) If the absorption be in excess of the expenditure, then Nature stores this energy up in the form of fat; if the expenditure be in excess of the absorption, then Nature works upon our bodies and we grow thin. If the absorption equal the expenditure, then we are in a state of what doctors term "physiological equilibrium" and perfectly good health. With the same degree of absorption, a pound of meat would enable us to perform (without any detriment to our system) a certain amount of work, two pounds twice that amount, and so on.

Our bodies are, in fact, delicately constructed heat-engines or machines-far more economical working ones, I would have you notice, than those artificial heatengines constructed by man; and, as Rumford has observed, you would get more work out of a ton of hay, if you gave it as food to a horse, than if you burned it in an engine. Nevertheless it is the combustion of the food in our system that furnishes the energy of our bodies, and there is no food capable of nourishing our bodies which, if well dried, is not capable of being burned in the fire.

From whence does this food derive its energy ? In every case from the SUN. If our food be vegetable food, then it is derived directly from the rays of the sun; if animal, the only difference is that it has built up the body of an animal before coming to us-the animal has eaten it and we have eaten the animal. From this source of energy-viz., food-is derived, of course, all those mechanical effects produced by the work of human beings and animals. The other sources of energy in Nature available to man for the production of mechanical effect are:

1. The energy derivable from rain.
2. The energy derivable from the tides.
3. The energy of the air in motion.
4. The energy of fuel.

With regard to the first-i.e., rain. This is due to the sun's rays vaporizing the water which, condensed again in hilly districts, becomes, in flowing under the action of gravitation down to a lower level, available for the production of work or mechanical effect. This is a most useful source of energy. where it is attainable.

Sir William Thomson-Lord Kelvinhas shown, however, that artificial elevated tanks would not give us so much energy as we should derive from the food grown

It has been proposed to transmit the power of Niagara electrically to long distances. Such a power as Niagara is indeed a mighty one if it could be utilized. It has been computed, I believe, that the power derived from our daily output of coal in the whole world is just about sufficient to pump the daily overflow of water back again. With this exception of Niagara, it does not appear, however, that any great mechanical effects could be derived from this source.

Recurring now to the energy derivable from tides''-due to the rotation of the moon around the earth. Although due to this cause, we must, however, remember that but for the radiant energy of the sun there would be no tidal energy whatever, because the seas and oceans would be one solid block of ice, for the earth's present supply of internal heat would not suffice to prevent the wrapping of this globe of ours in a winding-sheet of ice. We do sometimes take advantage of this tidal energy (due primarily, as I have shown, to the sun) by means of tidal mills, etc.; and quite recently the French have utilized the ebb and the flow of the tides at Havre to work turbine wheels, which generate the power necessary to work the dynamos which furnish Paris with the electric light. Generally speaking, however, but few places exist where this source of energy could be utilized.

Turning now to the energy derivable from the air in motion or the wind. Here, indeed, is a mighty power, among the first used by man, and which-though some may now think it rather old-fashioned-even yet forms a considerable portion of the energy used by man, as we perceive when we consider the number of sailing-vessels possessed by Britain and other countries, and the numerous windmills spread over the surface of the earth. This source of energy is due also to the radiant energy of the sun (the great heatengine of the solar system) resulting from an unequal distribution of heat over the earth's surface.

Lastly, we have "the energy derivable from fuel"-i.e., wood and coal, both produced by the sun, whose rays, decompos ing the carbonic-acid in the leaves of plants, set free the oxygen, while the carbon was used for the building up of the

woody fibre of the plant. So, too, with coal, which is only wood in another form. Their source of energy lies, of course, in the fact of the re-combination of the atoms of carbon and of the oxygen of the air caused by combustion. Here we have, indeed, a vast source of energy, but, nevertheless, one that man is doing his best to use up as quickly as possible.

The earth's forests and coal-fields, on the one hand, and her atmospheric oxygen on the other, constitute the earth's store of molecular energy for man-her capital, so to speak, stored up for his use; her income being her annual produce upon which the nations of old subsisted, but upon which we are no longer content to try and subsist.

By far the greater portion of the earth's crust (the only part which is of practical use to man) has long since parted with its energy. Granite, limestone, etc., as dynamic agents, or as a source of power to man, have been dead for ages; their atoms have long ago rushed together in chemical union and given up their molecular energy. Coal and wood, as I have already said, remain, but year by year more and more of the buried life stores of life-supporting and sustaining energy are being brought in larger and larger quantities to the earth's surface, and consumed with all speed more than eight million tons increase of coal being brought to the surface in Britain last year.

In ten or twelve generations-if not long beforehand-the available coal-fields of Great Britain will be exhausted. Similarly with regard to the existing woods and forests. These are being steadily and at an increasing rate wantonly destroyed, wantonly because it is quite possible so to arrange matters that the supply used cach year should be replaced by fresh growth during the same time. There ought to be a universal law that no man should cut down any tree without planting another in its place, not of course necessarily in the same spot. No fresh energy is being created by the earth. At her birth she possessed a certain amount which she has ever since been radiating into space like the sun, which we now know not to be an eternal light, though his life-duration is infinite, compared with that of the earth. Man, too, like the earth, creates nothing -neither matter nor force. No man ever made anything, he only shaped and

brought together or separated natural things already existing. The death of the earth and sun must both come, and with their death the end of all life upon this earth, but the human race of to-day is taking care that it shall cease to exist millions of years before either of these events come to pass. Having long ere this exhausted all that it has to live upon, it will have come to an untimely end. writer has most truly observed: spendthrift, the human race of to-day, boasting itself the heir of all the ages' in intelligence, is consuming at a rate really one hundred-fold beyond what is just the supplies which, as heirs of all the geological æons, it has received in trust partly for future generations."

As a

"Like a

No fallacy can be greater than to suppose that ANY scientific discovery can avert this disaster, because every such discovery only leads to a more rapid exhaustion of the earth's garnered stores.

Man in former times was the sport of the winds, the waters, and the seasons. Wars, pestilences, famines, disease, earthquakes, wild beasts, floods, etc. were his great destroyers, but by the instrumentality of science he has overcome these same destroyers, and grows, flourishes, and multiplies, increasing at such a rate that if our population increases at its rate of growth during the last twenty years (there are, however, signs of an increasing rate) it will amount in the year 2031-i.e., in 139 years, to more than three hundred millions, allowing about six square feet of earth-surface to each man.

The future of the United States is even worse than this. In four centuries, at their present rate of increase, supposing their population alone spread over the entire globe, each person would possess 27 square feet of earth surface.

The records of the birth and death-rates concerning which we are so prone to boast-show, though some of us are too short-sighted to see it, that man's untimely end (supposing no change to take place) must be even nearer than would be the case supposing that the consumption of the earth's life-supporting stores did not increase beyond its present rate.

These stores will last our time, you will say. True but have we not a debt to the future" as well as a "debt to the past"? Let this consumption, this wild waste-wild because it is being used to