A Modern Zoroastrian

by S. Laing

Conversely, if heat expands bodies, it is given out when they contract. Thus the enormous quantity of heat poured out for millions of years by the sun, is probably owing mainly to the mechanical force of contraction of the original cosmic matter condensing about the solar nucleus.

Again, when gases suddenly expand, their temperature falls, which is the principle by which artificial ice is procured, and frozen beef and mutton are brought from America and Australia, producing, such are the complicated relations of modern society, agricultural depression, fall of rents, and a serious aggravation of the Irish question.

As an example of the converse proposition of the transformation of heat into mechanical work, the steam-engine affords the aptest illustration. The original power came from the sun millions of years ago, and did work by enabling the leaves of plants to overcome the strong mutual affinity of carbon and oxygen in the carbonic dioxide in the air, and store up the carbon in the plant, where it remained since the coal era in the form of energy of position. By lighting the coal, or in other words separating its molecules more widely by heat, we enable them to exert once more their natural affinity for oxygen, and burn, that is recombine into carbonic dioxide. The heat thus produced turns water into steam, which passes through a cylinder, either into a condenser if the steam is at low pressure, or into the outer air if it has been superheated and brought to a higher pressure than that of the atmosphere. The difference of the pressure or elasticity of the steam in the boiler, and of the same steam when it is condensed or liberated, is available for doing work, and, being admitted and released alternately at the two ends of the cylinder, drives a piston up and down, which, by means of cranks and shafts, turns a wheel or does whatever work is required of it. In doing this, heat disappears, being converted into work, and the amount of heat would exactly equal that into which the work would be converted according to Joule’s law, if it could all be utilised without the loss necessarily incurred by friction, radiation, and the still more important absorption of latent heat required to convert water at boiling-point into vapour of the same temperature. This latter is not really an annihilation of the heat, but its conversion into work done in separating the molecules against the force of cohesion. The whole heat, therefore, is transformed into work, mainly molecular work in tearing molecules asunder, and the residue into mechanical work turning spindles and driving locomotives and steamboats.

The intermediate machinery here, including the water in the boiler, is merely the means of applying the original energy in the particular way we desire. The essential thing is the transformation of a certain amount of heat into work by passing, in accordance with the laws of heat, from a hotter to a colder body. The last condition is indispensable, for the nature of heat is to seek an equilibrium by passing from hot to cold, and no work can be got out of it in the reverse way. On the contrary, work must be expended and turned into heat to restore the temperature which has run down. The case is analogous to that of water, which, if raised by evaporation or stored up in reservoirs at a level above the sea, can be made to turn a wheel while it is running down; but when it has all run down to the sea level, can do no more work, and can only be pumped up again to a higher level by the expenditure of fresh work. Owing to this tendency of heat we can see that, although matter and energy are to all appearance indestructible, the present constitution of the universe is not eternal. The animating energy of heat is always tending to obliterate differences of temperature, and bring all energy down to one uniform dead level of a common average, in which no further life, work, or motion are possible. Fortunately this consummation is far off, and for many tens or hundreds of millions of years the inhabitants of this tiny planet may feel fairly secure, and need not, like the late Dr. Cumming, of millenarian celebrity, introduce breaks in the leases of their houses to provide against the contingency of the world coming to an end at an early date.

Dismissing, then, to the remote future any speculations as to the failure of this essential element of active energy, let us rather consider the various protean forms in which it shows itself.

1. The energy of visible motion, which, as we have seen, may be transformed into an equivalent amount of energy of position.

2. Molecular energy, which causes the cohesive attraction, repulsion, and other proper motions of these minute and invisible particles of matter.

3. Energy of heat and light, which are transmitted by waves of the assumed imponderable medium called ether.

4. Energy of chemical action, by which the small ultimate particles of ponderable matter, called atoms, separate and combine into the various combinations of molecules constituting visible matter, in obedience to certain affinities, or inherent attractions and repulsions.

5. Electrical energy, which includes magnetism as a special instance.