404 Prof. De Volson Wood on 



according to equation (20), 



t = 92 X 2 1 3 ° 12 =4x10 14 degrees F. 



(=400,000,000,000,000° F.). 



If the sun were composed of a substance having such spe- 

 cific heat, it could radiate heat at its present rate for more 

 than a hundred millions of centuries without its temperature 

 being reduced 1° F., exclusive of any supply from external 

 sources, or from a contraction of its volume. We know only 

 such substances in the sun as we are able to experiment with 

 in the laboratory; and if there be an exceptional substance in 

 it, Ave have no means at present of determining its physical 

 properties. It is, moreover, a question whether the aether 

 constitutes an essential part of bodies. We conceive of it 

 only as the great agent for transmitting light and heat through- 

 out the universe. 



On account of the enormous value of the specific heat, it 

 will require an inconceivably large amount of heat (mechani- 

 cally measured) to increase the temperature of one pound of 

 it perceptibly. Thus, if heat from the sun, by passing 

 through a pound of water at the earth, would raise the tem- 

 perature 100° F. and maintain it at, say, 600° F., absolute, 

 it would, under similar conditions, raise the temperature of 

 one pound of the aether, if its power of absorption be the same 

 as that of water, A6>Q00 l 00f000 of a degree*. 



The distance of the earth from the sun being 210 times 

 the radius of the latter, the amount of heat passing a square 

 foot of spherical surface at the sun will be about 45,000 times 

 the heat received on a square foot at the earth normally ex- 

 posed to its rays, so that, under the conditions imposed, the 

 temperature would not be a billionth of a degree F. higher at 

 the sun than at the earth. This, then, is a condition favour- 

 able to a sensibly uniform temperature even if heated by the 

 sun's rays. We are now inclined to admit that the aether is 

 not perfectly diathermanous to the sun's rays, but that its 

 temperature, however small, may be due directly to the 

 absorption of the heat of central suns ; for we begin to 

 realize the fact that the aether may possess many of the 

 qualities of gases, such as a molecular constitution, and 

 hence also mass, elasticity, specific heat, compressibility, 

 and expansibility, although the magnitude of these pro- 

 perties is anomalous. We have already considered its 



* This illustration is rather crude, since it discards the relative volumes 

 occupied by a pound of the respective substances. 



