1883.] Sir W. Siemens on Questions involved in Solar Physics. 315 



WEEKLY EVEXIXG MEETING, 



Friday, April 27, 1883. 



Geoege Busk, Esq. F.E.S. Treasurer and Vice-President, 



in the Chair. 



Sir William Siemens, D.C.L. LL.D. F.E.S. M.B.L 

 Some of the Questions involved in Solar Physics. 



The lecturer introduced his subject by drawing attention to the cir- 

 cumstance 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 suiTOunding the inhabitable surface by a non-conducting atmo- 

 sphere — the penumbra — to separate 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 00500^0000 P^^^ could fall 

 upon the sui-face of our earth, vegetation and force of every kind 

 being attributable to this radiation; whilst all but this fractional 

 proportion apparently went to waste. 



Eecent 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 comj)osed ; " but within only 

 seven years of that time Messrs. Buusen and Kirchhoft' j^ublished 

 their famous research, showing that by connecting the dark Fraun- 

 hofer 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. 



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