138 Transactions of the American Institute. 



which compose it into vapor, and thus forms about the nucleus an 

 enveloping layer of incandescent gas. Were this envelope seen alone, 

 it would give a spectrum of bright lines. In fact, however, we see 

 both together, and the white light of the nucleus, passing to our eyes 

 through this surrounding layer, has absorbed from it the precise lines 

 which would be given by the substances in this layer, and hence 

 reaches us containing these breaks or dark lines. To put this won- 

 derful theory to proof, an eclipse was necessary ; for the intense light 

 made it possible to see this envelope only when the moon came in as 

 a screen. With what interest, then, did astronomers look forward to 

 the total eclipse of 1868 to test the new hypothesis ! All the govern- 

 ments of Europe vied with each other in sending fully equipped 

 expeditions to the Indian Ocean ; and as the moment of totality drew 

 on, w r hat wonder that the observers were agitated and that their 

 nerves became tense. So soon as the last flash of sunlight disappeared, 

 bright lines appeared in the field of the spectroscope ! The proof 

 was conclusive that there was a colored envelope about the sun, and 

 Kirchhoff 's theory was essentially established. [By means of colored 

 photographs thrown on the screen, the lecturer illustrated his remarks 

 from time to time. He showed the original spectrum of Fraunhofer; 

 the remarkable spectrum obtained by photography by Rutherford ; 

 the coincidence of the sodium and D lines ; those jof the iron and 

 solar lines ; and the coincidence of the lines of several of the metals 

 with lines in the solar spectrum. With the electric light, Professor 

 Barker produced on the screen a continuous spectrum ; and then, 

 placing a piece of sodium on the lower carbon, the white-hot carbons 

 were surrounded by a layer of incandescent sodium vapor, and a black 

 band appeared on the screen in place of the yellow. The sodium 

 line was thus reversed and the production of the line D imitated.] 



Having now considered the spectroscope, and described the 

 method by which it may be applied to solar investigation, we may 

 pass to the sun itself, and consider briefly what has been revealed by 

 spectrum-analysis concerning its constitution. So long ago as the 

 eclipse of 1733, there were observed red, flame-like masses shooting- 

 out from the sun's edge. These were made the subject of special 

 attention in 1860 ; but their character remained a mystery until 1868, 

 when the spectroscope showed them to be masses of glowing hydrogen 

 gas, shooting out to a vast height from the solar surface. The 

 French astronomer Janssen, during the eclipse, conceived a method 

 by which these " protuberances " could be seen without an eclipse ; 

 the next day he put his plan into execution, and enjo} T ed for nine- 



