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XIII. On the Spectra of some of the 'Nebulae. By William Huggins, F.B.A.S. A 
Supplement to the Paper “ On the Spectra of some of the Fixed Stars. By William. 
Huggins, F.B.A.S., and W. A. Miller, M.B., LL.B., Treas. and V.P.B.S.” 
Communicated by Professor W. A. Miller, M.D. , LL.B. 
Received September 8, 1864, and printed in continuation of the paper preceding. 
The concluding paragraphs of the preceding paper refer to the similarity of essential 
constitution which our examination of the spectra of the fixed stars has shown in all 
cases to exist among the stars, and between them and our sun. 
It became therefore an object of great importance, in reference to our knowledge of 
the visible universe, to ascertain whether this similarity of plan observable among the 
stars, and uniting them with our sun into one great group, extended to the distinct 
and remarkable class of bodies known as nebulae. Prismatic analysis, if it could be 
successfully applied to objects so faint, seemed to be a method of observation specially 
suitable for determining whether any essential physical distinction separates the nebulae 
from the stars, either in the nature of the matter of which they are composed, or in the 
conditions under which they exist as sources of light. The importance of bringing 
analysis by the prism to bear upon the nebulae is seen to be greater by the consideration 
that increase of optical power alone would probably fail to give the desired information ; 
for, as the important researches of Lord Rosse have shown, at the same time that the 
number of the clusters may be increased by the resolution of supposed nebulae, other 
nebulous objects are revealed, and fantastic wisps and diffuse patches of light are seen, 
which it would be assumption to regard as due in all cases to the united glare of suns 
still more remote. 
Some of the most enigmatical of these wondrous objects are those which present in 
the telescope small round or slightly oval disks. For this reason they were placed by 
Sir William Herschel in a class by themselves under the name of Planetary Nebulae. 
They present but little indication of resolvability. The colour of their light, which in 
the case of several is blue tinted with green, is remarkable, since this is a colour 
extremely rare amongst single stars. These nebulae, too, agree in showing no indication 
of central condensation. By these appearances the planetary nebulae are specially 
marked as objects which probably present phenomena of an order altogether different 
from those which characterize the sun and the fixed stars. On this account, as well as 
because of their brightness, I selected these nebulae as the most suitable for examination 
with the prism. 
The apparatus employed was that of which a description was given at page 421. A 
second eyepiece was used in these observations, having a magnifying power of nine 
