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POPULAR SCIENCE REVIEW. 
metres broad. The following are the results of the micrometer readings for the 
less refrangible edge of the comet-band referred to the centre of the brightest 
portion of the carbon-band, which (with a narrow slit) is less than 5 tenth- 
metres broad : — 
1879. 
April 19 
28 
Comet-band. 
0-5 tenth-metres to blue 
4*5 „ to red 
Wave-length 
inferred. 
5190 
5191 
Width of slit, 
in. 
0*009 = 16 tenth-metres. 
0*013 = 24 
The wave-length of the less refrangible edge of the carbon-band (alcohol 
vapour in a vacuum tube) has been taken at 5198*3 tenth-metres. As it was 
not found practicable to use a narrower slit, there is probably an uncertainty 
of several tenth-metres in the position of the comet-band, but it appears 
from these observations that it coincides approximately with the band in the 
second spectrum of carbon (vacuum tube) at 5198, and not with that in the 
first spectrum (blue flame of Bunsen burner) at 5165. On April 17 several 
comparisons were made by Mr. Christie, by bringing up a movable bar from 
the blue end of the spectrum so as just not to hide the bright edge of the 
comet-band, and in every case the coincidence of the less refrangible edges 
of the comet and alcohol-bands appeared sensibly perfect. In these obser- 
vations the slit was of such a width that the bright line, with which the 
alcohol-band commences, had a breadth of about 30 tenth-metres. The 
principal comet-band extended about § of the way towards F, to about wave- 
length 5,000, its blue end appearing to coincide approximately with a faint 
band of alcohol. 
The second comet-band in the yellow was measured on April 28 by Mr. 
Maunder, and its red edge was found to be 2*4 tenth-metres to the red of 
the middle of the brightest part of the alcohol-band at 5610. The slit, how- 
ever, was very wide, viz. 0 in *033, corresponding to 65 tenth-metres. This 
measure would place the red edge of the comet-band at 5580, whilst the 
band in the first spectrum of carbon is at 5635. The more refrangible end 
of the yellow band appeared to coincide with a well-marked band in the 
alcohol spectrum. The third comet-band was very faint ; it appeared to be 
in the neighbourhood of the blue band of alcohol at 4835. The relative 
brightness of the three bands was estimated thus : Green, 10 ; Yellow, 3 ; 
Blue, £. 
At Lord Lindsay’s observatory' Dunecht, the following observations were 
made : — 
1879, April 12, at 12 h 9 m S.M.T.,the comet was well seen between clouds. 
It had a ray-like tail, which could be traced for about 25' from the highly 
condensed nucleus. The coma was obviously elongated at right angles to 
the direction of the tail, its greatest diameter being about 5'. Clouds pre- 
vented further observations. 
April 16, 10 h 30 m S.M.T., tail 10' long, in position 57°*8 by six measures 
with powers 122 and 229. No structure could be detected in the nucleus 
with powers 229 or 312. 
April 17, 12 h 56 m S.M.T., tail 13' long, in position 51°*9 from three 
measures with power 122. 
The spectrum was observed on April 16, May 2 and 3. 
