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propagated at the rate of about nine and a half million million kilometres 1 per year, and therefore twenty-eight and a half thousand million million kilometres in three thousand years. We do not know for certain whether the light which left the sun three thousand years ago is still travelling outwards with almost undiminished energy, or whether nearly all is already dissipated in heat, warming the luminiferous ether, or ponderable bodies which have obstructed its course. But we may, I think, feel almost sure that it is partly still travelling outwards as radiant heat, and partly spent (or dissipated) in warming ponderable matter (or ponderable matter and the luminiferous ether).

The running down of the weight in the clockwork has its perfect analogue, as Helmholtz was, I believe, in reality the very first to point out, in the shrinkage of the sun from century to century under the influence of the mutual gravitational attractions between its parts. The heat-producing efficiency of the fire which there would be if the sun

1 The "kilometre" is sixty-two hundredths of the British statute mile; rather a long half mile in fact.

were a globe of gunpowder or guncotton burning from its outward surface inwards-that is to say, the work done by the potential energy of the chemical affinity between uncombined oxygen, and carbon and hydrocarbons, attractive forces as truly forces, and subject to dynamic law, as is the force of gravity itself, is absolutely infinitesimal in comparison with the work done by the gravitational attraction on the shrinking mass adduced by Helmholtz as the real source of the sun's

heat.

The whole store of energy now in the sun, whether of actual heat, corresponding to the sun's high temperature, or of potential energy (as of the not run-down weight of the clockwork)—potential energy of gravitation depending on the extent of future shrinkage which the sun is destined to experience, is essentially finite; and there is much less of it now than there was three hundred thousand years ago. Similar considerations of action on a vastly smaller scale are of course applicable to terrestrial plutonic energy, and thoroughly dispose of the terrestrial "perpetual motion" by which

Lyell1 and other followers of Hutton, on as sound principles as those of the humblest mechanical perpetual-motionist, tried to find that the earth can go on for ever as it is, illuminated by the sun from infinity of time past to infinity of time future, always a habitation for race after race of plants and animals, built on the ruins of the habitations of preceding races of plants and animals. The doctrine of the "Dissipation of Energy" forces upon us the conclusion that within a finite period of time past the earth must have been, and within a finite period of time to come must again be, unfit for the habitation of man as at present constituted, unless operations have been and are to be, performed which are impossible under the laws governing the known operations going on at present in the material world.

1 Principles of Geology, vol. ii., edition 1868, p. 213 and pp. 40-243 (recapitulation of Chapters xxxi. and xxxiii., 1, 10, 15).

THE BANGOR LABORATORIES

[Address delivered on the occasion of the opening of the Physical and Chemical Laboratories in University College, Bangor, North Wales, February 2nd, 1885.]

I FEEL that the present occasion, upon which you have done me the honour to ask me to preside, is one of very great importance indeed, and I wish some person more competent to preside on such an occasion and give a suitable inaugural address were in my place. I am afraid I must confine myself to something not at all worthy of the greatness of an occasion which is almost the opening of a new university. Not quite so, because the real opening of this college took place several months ago; but still it is an occasion which I feel to be much more than merely the opening of a department—a working department—in the college; an occasion of so

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great moment that I regret that I shall not be able to give anything that could be properly considered a worthy inaugural address. I shall be obliged to ask your indulgence if I confine myself specially to departments with which I am personally familiar-scientific laboratories. The laboratory of a scientific man is his place of work. The laboratory of the geologist and of the naturalist is the face of this beautiful world. geologist's laboratory is the mountain, the ravine and the seashore. The naturalist and the botanist go to foreign lands, to study the wonders of nature, and describe and classify the results of their observations. But they must do more than merely describe, represent, and depict what they have seen. They must bring home the products of their expeditions to their studies, and have recourse to the appliances of the laboratory properly so-called for their thorough and detailed examination. The naturalist in his laboratory, with his microscope and appliances for the keenest examination, learns to know more than can be learned by merely looking at external

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