Scientific Lectures. 141 



forth concerning its nature ; the spectroscope, in the hands of Pro- 

 fessor Young, shows that it is a self-luminous gas, since it gives at 

 least one bright line which has become somewhat famous as the 1,474th 

 line, the number referring to its position upon Kirchhoff's scale. 

 The inner corona is unquestionably solar in its character ; and the 

 external corona is probably so, though the enormous distance to which 

 it extends makes it difficult to account for it. Many have considered 

 it a solar aurora ; and some plausibility has been given to this theory 

 by Winlock's observation, that a terrestrial aurora observed by him 

 gave a spectrum in which were three lines nearly or quite identical 

 in position with those observed in the solar corona by Young. The 

 1,474th line has been observed in the aurora but by one observer since 

 that time, however. On the whole, the character of the corona must 

 await further observations for its final determination. Much is hoped 

 for in this direction from the eclipse observed day before yesterday in 

 India, the first news from which Judge Daly has announced to us 

 to-night. It informs us only that the observations were successful. 

 [Photographs of the corona, as it appeared in the eclipses of 1868 

 and 1S69, were exhibited on the screen.] 



What now have we learned of the constitution of the sun by our 

 spectroscopic investigation ? In the first place, the theory of Sir 

 Wm. Herschel has been disproved. The sun can no longer be 

 regarded as having a cool, solid nucleus, inhabited by such beings as 

 ourselves, and surrounded by a luminous envelope. The first stratum 

 which is revealed to us is the photosphere. This KirchhofT supposes 

 to be liquid ; but from the remarkable mobility it possesses, and the 

 wonderful velocity with which changes take place in it, it is probably 

 gaseous, or at least vaporous. This is reconcilable with the results 

 of spectroscopic research, since Frankland has shown that a highly 

 condensed gas when incandescent may give a continuous spectrum. 

 This photosphere is in a state of intense activity, and glows with 

 all the fierceness of its enormously high temperature. Surrounding 

 this photosphere, and varying in thickness from one to twelve thou- 

 sand miles, is the chromosphere, composed of more rare vapors, but 

 which are yet incandescent. Here the absorption takes place which 

 gives the Fraunhofer lines. Here are the projections of hydrogen, 

 helium, sodium, magnesium, etc., which form the protuberances. 

 Here the cooling vapors of iron, barium, calcium and titanium from 

 the cloud, which, sinking down into the photosphere, forms a sunspot 

 and is finally swallowed up therein. Outside still of all this is 

 another atmosphere, constituting the inner and outer corona. The 



