SJK WILLIAM SIEMENS, F.R.S. 445 



SOME OF THE QUESTIONS INVOLVED IN 

 SOLAR PHYSICS. 



By SIR WILLIAM SIEMENS,* D.C.L., LL.T)., F.R.S., M.R.I. 



THE lecturer introduced his subject by drawing attention to the 

 circumstance that the idea of the sun being an exceedingly hot 

 body was of very modern date ; that both ancient and modern 

 writers up to the early portion of the present century attributed 

 to him a glorious and supernatural faculty of endowing us with 

 light and heat of the degree necessary for our well-being ; whilst 

 even Sir William Herschel had attempted to find an explanation 

 in justification of the time-honoured conception that the body of 

 the sun might be at a low temperature and inhabitable by beings 

 similar to ourselves, which he did in surrounding the inhabitable 

 surface by a non-conducting atmosphere the penumbra to sepa- 

 rate it from the scorching influence of the exterior photosphere. 



It was not till the views of Kant, the philosopher, had been 

 developed by La Place, the astronomer, in his famous " Mecanique 

 Celeste," that the opinion gained ground that our central orb was 

 a mass of matter in a state of incandescence, representing such an 

 enormous aggregate as to enable it to continue radiation into space 

 for an almost indefinite period of time. 



The lecturer illustrated by means of a diagram the fact that of 

 all the heat radiated away from the sun, only a2B o 1 00(;)00 part 

 could fall upon the surface of our earth, vegetation and force of 

 every kind being attributable to this radiation ; whilst all but this 

 fractional proportion apparently went to waste. 



Recent developments of scientific research had enabled us to 

 know much more of the constitution of the sun and other 

 heavenly bodies than had formerly been possible. Comte says in 

 his " Positive Philosophy " (Martineau's translation of 1853) that 

 " amongst the things impossible for us ever to know was that of 

 telling what were the materials of which the sun was composed ; " 

 but within only seven years of that time Messrs. Bunsen and 



* Excerpt Proceedings of the Royal Institution of Great Britain, 1883, pp. 

 315-321. 



