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LXXV. On the Spectra of some of the Nebula. By William 

 Huggtns, F.R.A.S. A Supplement to the Paper "On the Spec- 

 tra ofsomeoftheFixed Stars. By William Huggins, F.R.A.S., 

 and W. A. Miller, M.D., LL D., Treas. and V.P.R.S."* 

 [With a Plate.] 



THE concluding paragraphs of the preceding paper refer to 

 the similarity of essential constitution which our examina- 

 tion 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 de- 

 termining 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 pro- 

 bably 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 fan- 

 tastic 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 Her- 

 schel 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. 



* From the Philosophical Transactions for 1864, Part II. Communicated, 

 with additional notes, by the Author. 



