HISTORY OF THE CONSERVATION OF ENERGY 105 



density in his central parts." 25 " As for the future, . . . inhab- 

 itants of the earth can not continue to enjoy the light and heat essen- 

 tial to their life, for many million years longer, unless sources now 

 unknown to us are prepared in the great store-house of creation." 

 More detailed studies of the same subject were made in 1887, in a 

 lecture " On the Sun's Heat," delivered before the Eoyal Institution 

 of Great Britain. 26 



In this lecture Sir William Thomson refers to a very able paper, 

 " On the Theoretical Temperature of the Sun," by J. Homer Lane, 27 

 of Washington, which establishes the apparently paradoxical statement 

 that, within certain limitations, the more heat a gaseous body loses by 

 radiation, the hotter it will become. This theorem was discussed in 

 connection with the solar heat by Benjamin Peirce, 28 Simon New- 

 comb 29 and Sir Robert Ball. 30 Results similar to Lane's were reached 

 in the years 1878-83 in a series of very exhaustive papers by A. 

 Bitter. 31 A rival to the Helmholtz-Thomson theory of solar heat was 

 advanced about 1882 by William Siemens, 32 who imagined the rotating 

 sun to hurl, by centrifugal action at his equator, enormous quantities 

 of gas into space, which returned to him again at the poles. 



A refinement of the theory as presented by Helmholtz was intro- 

 duced in 1899 by T. J. J. See, 33 wherein he abandoned the Helm- 

 holtzian hypothesis of a sun of homogeneous density and, using Lane's 

 law, investigated minutely the more complex case of central condensa- 

 tion. Thereby the probable solar age was extended from about 18 

 to about 32 million years. 



Returning to the problem of the age of the earth, considered inde- 

 pendently of the sun, we find William Thomson the great moving 

 spirit. He approached the subject from more than one point of view. 

 One argument for limitation of the earth's age was based on the con- 

 sideration of underground heat. 34 " The heat which we know by 



25 Op. cit., p. 375. 



26 Op. cit., pp. 376-429. 



"American Journal of Science, 2d S., Vol. 50, 1870, pp. 57-74. 



28 Proceed. Am. Acad., XV., p. 201. 



29 "Popular Astronomy," 1st ed., p. 508; "The Stars," New York, 1901, 

 p. 210. 



30 "Story of the Heavens," London, 1893, p. 497. 



31 Wiedemann's Annalen, V., p. 405; X., p. 13; XI., p. 978; XII., p. 445; 

 XIIL, p. 360; XIV., p. 16; XVI., p. 166; XVII., p. 322; XVIIL, p. 488; 

 XX., pp. 137, 897. See Rosenberger, " Geschichte der Physik," Vol. III., 1887, 

 pp. 689, 690. 



32 " Ueber die Erhaltung der Sonnenenergie," Uebersetzt von C. E. Worms, 

 Berlin, 1885; see Rosenberger, "Geschichte der Physik," Vol. III., p. 687. 



33 Science, N. S., Vol. IX., 1899, pp. 737-740. 



34 W. Thomson, " The Doctrine of Uniformity in Geology Briefly Refuted," 

 read in 1865 before the Royal Society of Edinburgh. See Smithsonian Report, 

 1897, p. 343. 



