Dr. J. R. Mayer on Celestial Dynamics. 395 



right angles retain only ^^th part of their original intensity. 

 If it be further considered that our atmosphere absorbs a part of 

 the solar rays, it is clear that the rays which reach the tropics of 

 our earth at noonday can only possess from ^^th to g^^th of 

 the power with which they started. These rays, when gathered 

 from a surface of from 5 to 6 square metres, and concentrated 

 in an area of one square centimetre, would produce about the 

 temperature which exists on the sun, a temperature more than 

 sufficient to vaporize platinum, rhodium, and similar metals. 



The radiation calculated in Chapter III. likewise proves the 

 enormous temperature of the solar surface. From the determi- 

 nation mentioned therein, it follows that each square centimetre 

 of the sun's surface loses by radiation about 80 units of heat per 

 minute — an immense quantity in comparison with terrestrial 

 radiations. 



A correct theory of the origin of the sun's heat must explain 

 the cause of such enormous temperatures. This explanation can 

 be deduced from the foregoing statements. According to Pouillet, 

 the temperature at which bodies appear intensely white-hot is 

 about 1500° C. The heat generated by the combustion of one 

 kilogramme of hydrogen is, as determined by Dulong, 34,500, 

 and according to the more recent experiments of Grassi, 34,(366 

 units of heat. One part of hydrogen combines with eight parts 

 of oxygen to form water ; hence one kilogramme of these two 

 gases mixed in this ratio would produce 3850°. 



Let us now compare this heat with the amount of the same 

 agent generated by the fall of an asteroid into the sun. Without 

 taking into account the low specific heat of such masses when 

 compared with that of water, we find the heat developed by the 

 asteroid to be from 7000 to 14,000 times greater than that of 

 the oxy hydrogen mixture. From data like these, the extraordi- 

 nary diathermic energy of the sun's rays, the immense radiation 

 from his surface, and the high temperature in the focus of the 

 reflector are easily accounted for. 



The facts above mentioned show that, unless we assume on 

 the sun the existence of matter with unheard of chemical pro- 

 perties as a deus ex machind, no chemical process could maintain 

 the present high radiation of the sun ; it also follows from the 

 above results, that the chemical nature of bodies which fall into 

 the sun does not in the least affect our conclusions ; the effect 

 produced by the most inflammable substance would not differ by 

 one-thousandth part from that resulting from the fall of matter 

 possessing but feeble chemical affinities. As the brightest arti- 

 ficial light appears dark in comparison with the sun's light, so 

 the mechanical processes of the heavens throw into the shade the- 

 most powerful chemical actions. 



