246 Dr. J. R. Mayer on Celestial Dynamics. 



would become covered in a short space of time with a cold crust, 

 whereby radiation would be brought to an end. Considering 

 the continued activity of the sun through countless centuries, 

 we may assume with mathematical certainty the existence of 

 some compensating influence to make good its enormous loss. 



Is this restoring agency a chemical process ? 



If such were the case, the most favourable assumption w T ould 

 be to suppose the whole mass of the sun to be one lump of coal, 

 the combustion of every kilogramme of which produces 6000 

 units of heat. Then the sun would only be able to sustain for 

 forty-six centuries its present expenditure of light and heat, not 

 to mention the oxygen necessary to keep up such an immense 

 combustion, and other unfavourable circumstances. 



The revolution of the sun on his axis has been suggested as 

 the cause of his radiating energy. A closer examination proves 

 this hypothesis also to be untenable. 



Rapid rotation, without friction or resistance, cannot in itself 

 alone be regarded as a cause of light and heat, especially as the 

 sun is in no way to be distinguished from the other bodies of 

 our system by velocity of axial rotation. The sun turns on his 

 axis in about twenty-five days, and his diameter is nearly 

 112 times as great as that of the earth, from which it follows 

 that a point on the solar equator travels but a little more than 

 four times as quickly as a point on the earth's equator. The 

 largest planet of the solar system, whose diameter is about Yoth. 

 that of the sun, turns on its axis in less than ten hours ; a point 

 on its equator revolves about six times quicker than one on the 

 solar equator. The outer ring of Saturn exceeds the sun's 

 equator more than ten times in velocity of rotation. Never- 

 theless no generation of light or heat is observed on our globe, 

 on Jupiter, or on the ring of Saturn. 



It might be thought that friction, though undeveloped in the 

 case of the other celestial bodies, might be engendered by the 

 sun's rotation, and that such friction might generate enormous 

 quantities of heat. But for the production of friction two 

 bodies, at least, are always necessary which are in immediate 

 contact with one another, and which move with different velo- 

 cities or in different directions. Friction, moreover, has a 

 tendency to produce equal motion of the two rubbing bodies ; 

 and when this is attained, the generation of heat ceases. If 

 now the sun be the one moving body, where is the other ? and 

 if the second body exist, what power prevents it from assuming 

 the same rotatory motion as the sun ? 



But could even these difficulties be disregarded, a weightier 

 and more formidable obstacle opposes this hypothesis. The 

 known volume and mass of the sun allow us to calculate the 



