HISTORY OF THE CONSERVATION OF ENERGY 103 



did not attempt an estimate of the age of the solar system, but he 

 discussed the preliminary question as to the source of solar heat. As 

 soon as Mayer had convinced himself that energy can not be destroyed, 

 and that the energy of the earth comes mainly from the sun, he began 

 to study what Sir William Herschel had called " the great secret " of 

 the maintenance of solar heat. In 18-11, before the publication of his 

 first paper, he asked questions relating to solar heat, in a letter to 

 Baur, " Is it the glowing of the sun ? Why does he not cool off ? 

 Is it a burning depending upon willing meteoric stones ? " 21 



In 1816 he had a paper ready on this subject. Being reminded by 

 a friend that no one can be a prophet in his own country, he sent the 

 paper to the Academy of Sciences in Paris. A committee of the 

 academy was directed to report on this paper, but it failed to do so 

 and the paper was ignored. It could be published only at his own 

 expense. It appeared in 1818 under the title, " Celestial Dynamics." 

 Mayer concludes that the sun can not be a glowing mass, sending out 

 radiation without compensation; solar heat can not be due entirely to 

 chemical changes; solar heat can not be due to solar rotation. He 

 finally embraces the theory that solar heat is due to the energy of 

 meteors falling into the sun. He did not overlook the fact that the 

 resulting increase of mass of the sun would increase its attraction for 

 the planets, and would shorten the sidereal year. He knew that ob- 

 servation does not disclose any variation in the length of the year. 

 An easy explanation would be offered by Newton's corpuscular theory 

 of light, ^according to which the sun sends out matter into space. But 

 this theory was then known to be untenable. In this dilemma Mayer 

 takes refuge in an idea which rests on a misconception of the unclula- 

 tory theory of light, and he offers an explanation which is now easily 

 recognized as invalid. 



From Mayer we pass to William Thomson, the late Lord Kelvin, 

 who, six years later, took up the very same problem and arrived inde- 

 pendently at almost identically the same conclusions. That solar heat 

 may be due to falling meteors was first suggested in England by 

 Waterston. Unlike Mayer, Thomson sees no objection to the increase 

 in the sun's mass resulting from meteoric showers, for, " according to 

 the form of the gravitation theory " which he proposed, " the added mat- 

 ter is drawn from a space where it acts on the planets with very nearly 

 the same forces as when incorporated in the sun." In an appendix to 

 the paper, Thomson ventures an estimate of the age of the sun. This is 

 the first attempt, made by a physicist, to compute the age of our great 

 luminary and to prepare a mortuary estimate of it. He goes on the 

 supposition that the solar energy of rotation is derived from the energy • 

 of falling meteors. He calculates that, allowing for the constant loss 



21 " Mechanik der Warme," p. 146. 



