120 



Anniversary Meeting. 



[Nov. 30, 



point for mathematical investigations relating to the corpuscular theory. 

 It is much to be regretted that Professor Plateau's scientific labours for 

 more than twenty years past have been carried on under a deprivation of 

 sight occasioned by the ardent pursuit of his favourite science. Although 

 totally blind, his experiments are of the most exquisite delicacy ; and the 

 reasoning of which they form the material is as accurate and penetrating 

 as the experiments themselves are beautiful. 



The second gentleman who is elected a Foreign Member, Professor 



o 



Angstrom, is distinguished by his researches in many departments of physical 

 science, and is entitled to rank among the very highest of those who have 

 within a few years developed the powers of spectroscopy to their present 

 marvellous extent. In fact, his ' Optic Researches,' 1853, contain the 

 fundamental principles of nearly all that has been done since. 



The following notice is from the pen of the Rev. Dr. T. Romney Robin- 

 son, F.R.S., of Armagh : — 



" From Euler's theory of Resonance, he infers that, as a body absorbs all 

 " the series of oscillations which it can itself assume, it must, when heated so 

 " as to become luminous, emit the same rays which at a lower temperature it 

 " absorbs. 



" It is hardly possible to announce more distinctly this important fact, on 

 " which nearly all solar and stellar spectroscopy rests ; and it is much to be 

 " regretted that, from the ignorance of the Scandinavian languages which is 

 " so general in this country, it was not known here till 1856. He proceeds 

 " to examine the spectrum of the electric spark. It is traversed by two sets 

 "of lines on an obscure ground. The first of these belongs to air. The 

 " lines reach across the spectrum, and do not vary with the nature of the 

 " electrodes. The second set come from the electrodes ; they are in general 

 " far brighter than the other, and, unless the discharge is powerful, are con- 

 " fined to the vicinity of the electrodes. Each metal has its own set ; but, 

 "owing to the small dispersion of his spectroscope (one prism of 46°), he 

 " thought some lines were common to two or more metals. Alloys showed 

 "the lines of their components with no greater difference than could be ex- 

 plained by the want of power in his instrument. He shows that these 

 " lines are not produced by interference. The solar spectrum may be re- 

 " garded as a reversion of the electric one ; and he is convinced that the ex- 

 " planation of the dark lines in the former embraces that of the bright 

 " lines in the other. Each gas has its peculiar spectrum ; he notices the 

 " faintness of the oxygen-lines in air, and he describes the three bright bands 

 " of hydrogen, and a fourth fainter. 



"In 1861, in a second memoir, he developed 1 is theory of the reversion of 

 " the lines. He had then obtained a better spectroscope and a large Ruhm- 

 " korff, with which he compared many of the solar with metallic lines. Many 

 " double lines belong to two metals. Gas-lines are more diffused and less 

 " sharply defined than those of metals, especially metals difficult of fusion. 

 " He found no evidence of nitrogen or oxygen in the sun. 



