1889.] of the various Species of Heavenly Bodies. 199 



the manganese absorption was increasing, whilst the carbon was 

 probably beginning to fade ont. 



The later observations of Vogel, on June 22nd, and of Christie,* 

 between July 3rd and 14th, are incomplete, inasmuch as the positions 

 of all the bands were not determined. Yogel gives the position of the 

 green band as 51-5, but simply states the presence of the citron and 

 blue band. Christie states that two of the bands were sensibly coinci- 

 dent with the two principal bands in the spectrum of carbon dioxide 

 (probably carbon 517 and 474), but the position of the third band 

 was not determined. It is scarcely possible, therefore, to say how far 

 the indications of manganese absorption have increased between 

 June 22nd and July 14th. Christie states, however, that there was 

 line absorption on July 14th, six days after perihelion. I have stated 

 in another part of the paper that the highest temperature effects do 

 not occur until the comet is some distance beyond perihelion, and this 

 is a case in point. 



As Coggia's Comet approached perihelion, therefore, after having 

 first become visible, the first recorded change in its spectrum was the 

 addition of manganese absorption to carbon radiation, but the dis- 

 cussion of other cometary spectra shows that there was probably an 

 intermediate stage between June 4th and June 7th, when instead of 

 manganese absorption, manganese radiatio'n was added. A little later 

 cool carbon absorption was added. Finally, just after perihelion, 

 fluting was replaced by line absorption. 



In observations in my own observatory with my 6-inch refractor, 

 I obtained indications that the blue rays were singularly deficient in 

 the continuous spectrum of the nucleus of the comet ; and in a com- 

 munication to ' Nature 'f I suggested that this fact would appear to 

 indicate a low temperature. 



This conclusion was strengthened by observations which I made at 

 Newcastle with Mr. Newall's telescope. The colour, both of the 

 nucleus and of the head of the comet, as observed in the telescope, was 

 of a distinct orange yellow, and this, of course, lends confirmation to 

 the view expressed above. While ten minutes' exposure of a photo- 

 graphic plate gave no images of the comet, the faintest of seven stars 

 in the Great Bear gave an impression in two minutes. 



The fan also gave a continuous spectrum but Httle inferior in 

 brilliancy to that of the nucleus itself ; while over these, and even the 

 dark space behind the nucleus, was to be seen the spectrum of bands,, 

 which indicates the presence of a rare vapour of some kind, while the 

 continuous spectrum of the nucleus and fan, less precise in its indi- 

 cations, may be referred either to the presence of denser vapour or 

 solid particles. 



* ' Greenwich Observations,' 1875, p. 121. 

 f ' Nature,' vol. 10, p. 180, 1874. 



