198 Mr. J. N. Lockyer. On the Classification [Jan. 10, 



The later observations of Gothard* and Konkoly,f showed nothing 

 but the three ordinary bands. \.- 



No observations were made after the comet had got sufficiently 

 cool to show either the cool carbon flutings or the magnesium fluting 

 at 500. 



Although the observations are not perfectly continuous, there is 

 conclusive evidence that the reduction in temperature of the comet 

 consequent on its departure from the neighbourhood of the sun was 

 accompanied by the following changes in its spectrum : 



18th September. Bright and dark iron lines and manganese 

 flutings. 



29th September. Bright flutings of iron. 



22nd October. Bright manganese. 



1st November. Hot carbon radiation. 



The two latter stages have already been specially referred to (p. 193). 



No doubt if further observations had been possible the flutings of 

 hot carbon would have been replaced by cool carbon flutings, and these 

 again by magnesium 500. 



CoggicCs Comet. 



The perihelion passage of this comet occurred on July 8th, 1874, 

 and the available observations of its spectrum date from May 18th to 

 July 14th. On May 18th, Vogel J observed three bands, one of which 

 was at wave-length 515. This was probably the hot carbon fluting at 

 517, but as the wave-lengths of the other bands are not given, it is 

 not possible to come to a definite conclusion. 



On the 18th May Yogel again recorded the three bands, the prin- 

 cipal one commencing at 516'5, and having a second maximum at 512. 

 It is probable that these were the first two maxima of the green carbon 

 band, the wave-lengths of which are about 517 and 513. 



On June 4th, the date of Yogel's next observation, the three bands 

 were still visible. The wave-lengths are given as 562, 514, and 473. 



On June 7th, Yogel's observation recording three bands at 557, 518, 

 and 473, give evidence of manganese absorption, as indicated by the 

 apparent displacement of the citron carbon band in the manner I have 

 already explained. 



On June 13th, 14th, and 15th, in addition to the absorption of man- 

 ganese, there was probably the absorption of cool carbon, as indicated 

 by the masking of the 2nd maximum of the citron carbon band, as I 

 have already explained. 



D ' Arrest's observations on June 15th, 16th, and 17th, show that 



* ' Astr. Nachr.,' No. 2472 and 2716. 

 t 'Astr. Nachr.,' No. 2475. 

 J ' Astr. Nachr.,' No. 2018. 

 ' Astr. Nadir.,' No. 2001. 



