446 THE SCIENTIFIC PAPERS OF 



Kirchhoff published their famous research, showing that by con- 

 necting the dark Fraunhofer lines of the solar spectrum with the 

 bright lines observed in the spectra of various metals, it was 

 possible to prove the existence of those substances in the solar 

 photosphere, thus laying the foundation of spectrum analysis, the 

 greatest achievement of modern science. Dr. Huggins and others, 

 applying this mode of research to other heavenly bodies, including 

 the distant nebulas, had extended our chemical knowledge of them 

 in a measure truly marvellous. 



Solar observation had thus led to an analytical method by which 

 chemistry had been revolutionised ; and it would be, in the lec- 

 turer's opinion, through solar observation that we should attain to 

 a much more perfect conception of the nature and effect of radiant 

 energy in its three forms of heat, light, and actinism, than we 

 could as yet boast of. The imperfection of our knowledge in this 

 respect was proved by the circumstance that whereas some astro- 

 nomers and physicists, including Waterston, Secchi, and Ericsson, 

 had, in following Sir Isaac Newton's hypothesis, attributed to the 

 sun a temperature of several millions of degrees Centigrade, others, 

 including Pouillet and Yicaire, in following Dulong and Petit, had 

 fixed it below 1500 C. Between these two extremes, other deter- 

 minations, based upon different assumptions, had fixed the solar 

 temperature at between 60,000 and 9000. 



The lecturer having conceived a process by which solar energy 

 may be thought to a certain extent self-sustaining, had felt much 

 interested for some years in the question of solar temperature. If 

 the temperature of the solar photosphere should exceed 3000 C., 

 combustion of hydrogen would be prevented by the law of dis- 

 sociation, as enunciated by Bunsen and Sainte-Claire Deville ; and 

 his speculative views regarding thermal maintenance must fall to 

 the ground. To test the question, he in the first place mounted a 

 parabolic reflector on a heliostat with a view of concentrating solar 

 rays within its focus, which, barring comparatively small losses by 

 absorption in the atmosphere and in the metallic substance of the 

 reflector, should reproduce approximately the solar temperature. 

 By introducing a rod of carbon through a hole at the apex of the 

 reflector until it reached the focus, its tip became vividly luminous, 

 producing a light comparable to electric light. When a gas-burner 

 was arranged in such a way that the gas flame played across the 



