THE SUN'S HEAT.

Daily Telegraph (Napier), Issue 3055, 11 April 1881, Page 4

THE SUN'S HEAT.

_LOW IT IS MAINTAINED— HOW LONG IT IS „IKW/Y TO LAST. How is the heat of the sun maintained ? How long has ifc lasted ? How long will it continue ? Two theories are advanced. The first that the heat is caused by ME PLANETS FALLINO INTO THE SUN. From its present orbit, by which it appears that Jupiter would maintain the sun s present expenditure of energy for 32,254 years and Mercury for six years and 219 days, and that the collapse of all the planets upon the Bun would generate sufficient heat to maintain its supply for nearly 46,000 years ; and after estimating that matter equal to only about one one-hundredth part of the mass of the earth, falling annually upon the solar Biirface, would maintain its radiation indefinitely, Professor Young thinks it improbable, from astronomical reasons, that any such quantity of matter can be supposed to reach the sun. So largo a quantity of matter would necessitate a vastly greater quantity circulating around the sun, between it and the planet Mercury. But if there were near the sun meteoric matter equalling, for example, the mass of the earth, it ought to produce an observable effect on the motions Of Mercury, and no such effect has yet been made. Astronomers, therefore, failing to find a full explanation of the cause of solar energy in this hypothesis, have adopted a second one, which is thafe THE SUN'S DIAMETEB IS SLOWLY CONTEACTING. And that the gaseous mass is gradually liquifying and becoming solid. The conclusion is drawn that if this theory be correct there must come a time when there will be no solar heat, as there has also been a time when it began. How far forward is the end, how far backward the beginning. Newcomb is authority for the statement that with its present radiation the sun will shrink to half its present diameter in about 5.000 000 years. Reduced to this size, and eight times as dense as now, ifc will cease to be mainly gaseous, and its temperature would begin to fall. Hence Newcomb assigns as the term during which the sun can supply heat enough to support life on the earth, as we know life, a period of 10,000,000 years. The writer somewhat more confidently casts his eye backward, and concludes that the sun cannot have been emitting heat at the present rate for more than 18,000,000 years, if its heat has been generated in the manner described. The possibility of collision with wandering stars, and suggestion of ways as yet unconceived of for restoring wasted energy, are followed by the statement that " the present order of things appears to be limited in either direction by terminal catastrophes which are veiled in clouds as yet impenetrable."