1889.] of the various Species of Heavenly Bodies. 



173 



The result is an apparent displacement of the 564 fluting, whilst the 

 517 fluting retains its position. This is by far the most general case 

 of masking in comets. 



D'Arrest (' Astr. Nachr.,' No. 2001, p. 138), speaking of Coggia's 

 Comet, says : " The centre shows a bright continuous spectrum with 

 some dark absorption bands." This observation was made on June 

 15th, and the perihelion passage of the comet took place on July 8th, 

 1874. The statement is so indefinite, however, that to determine the 

 origin of the bands is almost out of the question. It is probable that 

 one of the bands at least was due to manganese. The above view is 

 strengthened by the fact that Vogel's observation on June 15th (* Astr. 

 Xachr.,' vol. 85, p. 19) gave indications of manganese absorption. 



There is another interesting point in connexion with manganese. 

 In the second part of this Appendix I show that the principal 

 aurora line (557) is in all probability the remnant of the manganese 

 fluting at 558, and hence there is a close relation between the spectrum 

 of the aurora and cometary spectra. Professor Young recognised 

 this relation as far back as 1872, but he attached no importance to it. 

 In a note on Encke's Comet he states that, "Although quite probably 

 merely accidental, it may be also worth noting that the principal line 

 of the aurora spectrum (wave-length 5568) very closely coincides 

 with the lowest (cometary) band." 



Lead Absorption. 



In other cases we have, in addition to the absorption of manganese, 

 the absorption of the lead fluting at 546. The result of this is a much 

 greater apparent shifting of the carbon fluting at 564, as shown ' in 

 fig. 6. In the absence of the carbon fluting 564, which is not so 



If 'Monthly Notices,' vol. 37, p. 432. 

 ** ' Astr. Nachr.,' vol. 92, p. 301. 

 ft ' Copernicus,' vol. 2, p. 223. 

 JJ ' Copernicus,' vol. 2, p. 223. 

 'Amer. Journ.,' vol 3, Feb., 1872. 

 N 



* ' Spectra der Cometen,' p. 24. 

 t ' Phil. Trans.,' vol. 158, p. 556. 



I ' Bothk. Beob.,' vol. 1, p. 62. 



' Amer. Journ. Sci.,' vol. 3, p. 81. 



II 'Astr. Nachr.,' vol. 85, p. 12. 

 VOL. XLV. 



