﻿456 Mr. W. Huggins on some Spectrum 



than the second power are omitted, members are wanting in the 

 result which should not be omitted ; and therefore this result 

 cannot, until otherwise proved, lay claim to any validity. 



I think I have thus shown that all the investigations cited at 

 the outset of my paper, however cleverly they otherwise treat the 

 matter, contain certain faults which make it impossible to admit 

 that the results are correctly deduced, and that the solution of 

 the problem of referring electrodynamic forces to known electro- 

 static forces has not been attained in these investigations. 



Wiirzburg, October 20, 1868. 



LXIII. On some Spectrum Observations of Comets. 

 By William Huggtns, F.R.S.* 



THERE is another class of heavenly bodies distinct from the 

 objects we have considered — the comets. Of the nature 

 of the phenomena presented by these strange masses of light of 

 constantly changing form we possess but little certain informa- 

 tion. It is doubtless to spectrum analysis that we must look for 

 any important increase of our positive knowledge of the consti- 

 tution of those bodies, and of the true nature of the remarkable 

 changes which take place in them under the action of the solar rays. 



A not unimportant earnest of the more complete information 

 which the prism will doubtless exact from the next brilliant comet 

 has been already gained by the examination of five faint comets. 

 One of these was examined by Donati in 1864f. Two of these, 

 which were excessively faint, I observed in 1866 J and 1867 §. 

 The others, which were in a small degree brighter, I examined 

 in the summer of last year. 



These observations showed that the greater part of the light 

 from the heads of comets is very different from solar light, and 

 therefore cannot be the sun's light sent to us by ordinary re- 

 flection from the cometary matter. 



In the case of the very faint comets of 1866 and 1867, I was 

 not able to determine more than that the light of the brightest 

 part of the coma consisted for the most part of green rays of the 

 refrangibility between b and F of the solar spectrum. Further, 

 as far as such very faint objects would permit of observation, I 

 suspected that the margin of the coma and the tail gave a conti- 



* From the Rede Lecture, delivered at Cambridge, May 18, 1869. 

 Communicated by the Author. 



t Astronomische Nachrichten, No. 1488 ; and Monthly Notices of the 

 Royal Astronomical Society, vol. xxv. p. 490. 



X Proceedings of the Royal Society, vol. xv. p. 5. 



§ Monthly Notices of the Royal Astronomical Society, vol. xxvii. p. 288. 



