1869.] The Presidents Address. 581 



cases so remarkable as to establish almost to a certainty the exist- 

 ence of several of the known elements in the solar atmosphere, 

 producing by their absorbing action the dark lines coinciding with 

 the bright lines observed. Among other elements may be mentioned 

 in particular hydrogen, the spectrum of which, when traversed by 

 an electric discharge, shows a bright hne or band exactly coinciding 

 with the dark line C, and another with the line F. 



Now Mr. Huggins found that several of the stars show in their 

 Bjiectra dark lines coinciding in position with C and F, and what 

 strengthens the belief that this coincidence, or apparent coincidence, 

 is not merely fortuitous, but is due to a common cause, is that the 

 two lines are found associated together, both present or both absent. 

 And Kirchhoff's theory suggests that the common cause is the 

 existence of hydrogen in the atmospheres of the sun and certain 

 stars, and its exercise of an absorbing action on the hght emitted 

 from beneath. 



Now by careful and repeated observations with a telescope 

 furnished with a spectroscope of high dispersive power, Mr. Huggins 

 found that the F line, the one selected for observation, in the 

 spectrum of Sirius, did not exactly coincide with the corresponding 

 bright line of a hydrogen spark, which latter agrees in position 

 with the solar F, but was a little less refrangible, while preserving 

 the same general appearance. 



Assuming, then, that the small difference of refrangibihty 

 observed between the solar F and that of Sirius is due to proper 

 motion, Mr. Huggins concludes from his measures of the minute 

 difference of position that, at the time of the observation, Su'ius 

 was receding from the earth at the rate of 41 "4 miles per second. 

 A part of this was due to the motion of the earth in its orbit, and 

 on deducting the orbital velocity of the earth, resolved in the 

 direction of a line drawn from the star, there remained 24 • 4 miles 

 per second as the velocity with wliich Sirius and our sun are 

 mutually receding from each other. 



We turn now to another recent apphcation of spectral analysis. 

 Various expeditions were equipped for the purjDOse of observing the 

 total solar eclipse which was to happen on the 17th August, 1868, 

 and shortly before the conclusion of the meeting of the Association 

 at Norwich last year, the first results of the observations were made 

 known to the meeting, through the agency of the electric tele- 

 graph. In a telegram sent by M. Janssen to the President of the 

 Royal Society, it was announced that the spectrum of the promi- 

 nences was very remarkable, showing bright lines, while that of 

 the corona showed none. The prominences could not be clouds in 

 the strict sense of the term, shining either by virtue of their own 

 heat or by light reflected from below. They must consist of 

 incandescent matter in the gaseous form. It appears from more 



