A Modern Zoroastrian

by S. Laing

To pursue this farther would lead us far astray into the misty realm of metaphysics, and I refer to it only as showing that the principle of the conservation of energy, standing as it does in apparent contradiction to our natural impressions, requires a fuller demonstration than the kindred principle of the indestructibility of matter.

In the case of ordinary mechanical power it had been long known that the intervention of machinery did not create force, but only transformed it. If a weight of 1 lb., A, just balances a weight of 2 lb., B, by aid of a pulley, and by the addition of a minute fraction, such as a grain, raises it 1 foot, it will be invariably found that A has descended 2 feet. In other words, 1 lb. working through 2 feet does exactly the same work as 2 lbs. working through 1 foot. And whatever may be the intervening machinery the same thing holds good, and the work put in at one end comes out, neither more nor less, at the other, except for a minute loss due to friction and resistance of air. If a force equal to 1 lb. is made, by multiplying the intermediate machinery, to raise a ton a foot from the ground, exactly as much force must have been exerted as if the ton had been divided into 2,240 parts of 1 lb. each, and each part separately lifted.

But although energy cannot be created, at first sight it seems as if it might be destroyed, as when the ton falls to the ground and seems to have lost all its energy, whether of motion or of position. But here science steps in and shows us that it is not destroyed, but simply transformed into another sort of motion, which we call heat.

Some connection between mechanical work and heat had long been known, as in the familiar experiment of rubbing our hands together to warm them; and the practice known to most primitive races of obtaining fire by twirling a stick rapidly in a hole drilled in a block of wood; a practice described by the old Sanskrit word ‘pramantha,’ which means an instrument for obtaining fire by pressure or friction, and which, translated into Greek, has been immortalised by the legend of Prometheus. But it was reserved for recent years, and for an English philosopher, Dr. Joule, to give scientific precision and generality to this idea, by actually measuring the amount of heat produced by a given amount of work, and showing that they were in all cases convertible terms, so much heat for so much work, and so much work for so much heat. He did this by measuring accurately by a thermometer the heat added to a given amount of water by the work done by a set of paddles revolving in it, set in rapid motion by a known weight descending through a known space. The unit of work being taken as that sufficient to raise 1 kilogramme through 1 metre, and that of heat as that required to raise the temperature of one kilogramme of water by 1° Centigrade, the relation between them, as found by a vast number of careful experiments, is that of 424 to 1. That is, one unit of heat is equal to 424 units of work.

In this, and all cases requiring scientific precision, it is better to use the units of the metrical system than our clumsy English standards; but it may be sufficient for the ordinary reader to take the metre, which is about 39·37 inches, as practically a yard, and the kilogramme, which is 15,432 English grains, as practically equal to 2 lbs. This is sufficient to show the much greater energy of the invisible forces which act at minute distances, than that of gravity and other forces which do appreciable mechanical work, the energy of a weight falling from a height of more than 1,300 feet being only sufficient to heat its own weight by 1°.

This proof of the convertibility of work into heat gives much greater precision to our ideas respecting the real nature of heat and its kindred molecular and atomic energies. Heat is clearly not a material substance, for a body does not gain weight by becoming hotter. In the case of all ponderable matter down to the atoms, which are only of the size of cricket-balls compared to that of the earth, any combination which adds matter adds weight, and the weight of the product exactly equals the sum of the weights of the separate factors which have united to form it. Thus, if iron is burnt in oxygen gas, the product, oxide of iron or rust, weighs more than the original iron by just as much as the weight of the oxygen which has been consumed. But heat, light, and electricity add nothing to the weight of a body when they are added to it, and take nothing away when they are subtracted. The inference is unavoidable that heat, like light, is not ponderable matter, but an energy transmitted by waves of the imponderable medium known as ether. This is confirmed by finding that when a ray from the sun is analysed by passing through a refracting prism, one part of the spectrum shows light of various colours, while another gives heat. The hottest part of the spectrum lies in the red and beyond it, showing that the heat-waves are longer, and their oscillations slower, than those of light. Heat-waves also may be made to interfere, and to become polarised, in a manner analogous to the phenomena exhibited by those of light.

There can be no doubt, therefore, that heat, like light, is an energy or mode of motion, transmitted by waves of an imponderable ether, and that it acts on the molecules and atoms of matter by the accumulated successive impulses of those waves on the molecules and atoms which are floating in it, or rather which are revolving in it, in definite groups and fixed orbits, like miniature solar systems or starry universes. We can now see how heat performs work, and why work can be transformed into it.

Heat performs work in two ways. First, it expands bodies—that is, it draws their molecules farther apart against the force of cohesion which binds them together or keeps them moving in definite orbits at definite distances. It is as if it increased the velocity, and therefore the centrifugal force of a system of planets, and so caused them to revolve in wider orbits. The expansion of mercury in a thermometer affords a familiar instance of this effect of heat and the readiest measure of its amount. Secondly, it increases the energy of the molecular motions, so that they dart about, collide, and vibrate with greater force. Thus, as heat increases, evaporation increases, for molecules on the surface are projected with so much force as to get beyond the sphere of the cohesive attraction which binds them to the system, and they dart off like comets into space. Finally, as heat increases, and more and more work is done, against the centripetal force of cohesion, most substances, and doubtless all if we could get heat enough, are converted from solids into fluids, and ultimately into gases, in which latter state the molecules have got altogether beyond the sphere of their mutual attraction, and tend to dart off indefinitely in the direction of their own proper centrifugal motions, unless confined, in which case they dart about, collide, rebound, and exercise pressure on the containing surface.