THE SUN'S HEAT.

Auckland Star, Volume XVIII, Issue 69, 23 March 1887, Page 3

THE SUN'S HEAT.

It Will Last 10,C00,000 Years as li

is Now.

A BKILLLINI audience filled the theatre of the Royal Institution last night (January 21st) while Prof. Sir William Thomson expounded the latest dynamical theories regarding tho ''probable origin, total amount, and possible duration of tho sun's heat." During the short 3,000 years or more of which man possesses historic records thero was, the learned physiciat showed, no traco of variation in solar energy ; and tliero was no distinct ovidence of it even, thcugh the earth as a whole, from being nearer the sun, received in January 6i per cent, more heat than in July. But in the inilliooß of yeara which geology carried us back, it might safely be paid there must have been great changes. How had the Bolar fires been maintained during those ages? The scientific answer to this question was the theory of Helmholtz that thßßun was a vast globe gradually cooling, but as it cooled gradually shrinking, and that the shrinkage - which was the effect of gravity upon its mass—kept up its temperature. The total of the sun's heat was equal to that which would be required to keep up 476,000 millions of millione of millions of horse-power, or about 78,0i10 horss power for every metre a little more than a square yard—and yet the modern dynamical tht ory of heat shows that the sun's mass would require only to fall in or contract thirty-fivH^uetres per annum to keep up that tremendous energy. At this rate the solar radius in 2,000 years' time would be about 100 per cent, less than at present. A time would come when the temperature would fall, and it was thus inconceivable that the sun would continue to emit heat sufficient to sustain existing life on the globo for more than 10,000,000 years. Applying tho fame principles retrospoctively, they could not suppose that the sun had existed for more than 20,000,000 yoar? — no matter what might have been its origin whether it eamo into existence from tho clash of worlds pre-existing, or of diffused nobulouß matter. There was a great clinging by geologists and biologists to vastly lODger periods, but the physicist, treating it aßa dynamic question with calculable elemonts, could come to no other conclusion materially different from what he had stated

Sir William Thomson declined to discuss any chemical source of heat, which, whatever its effect wheo primeval elements first eamo into contact, was absolutely insignjficaut compared with tho effects of gravity after globes like the sun and the earth had been formed. In all these speculations they were in the end driven to the ultimate elements of matter—to the question—when they thought what became of all the sun's heat—what is the luminiferous ether that fills space, and to that most wonderful of forces upon which Faraday spant so much of the thought of his later years, gravity.— " London Telegraph."