40 Mr. W. Huggins on the Spectrum [Jan. 26, 



gaseous form, are 57 M, the annular nebula in Lyra, and 27 M, the Dumb- 

 bell nebula. The results of the examination of these nebulae with telescopes 

 of great power must probably be regarded as in favour of their consisting 

 of clustering stars. It was therefore of importance to determine, by the 

 observation of other objects, whether any nebulae which have been certainly 

 resolved into stars give a spectrum which shows the source of light to be 

 glowing gas. With this purpose in view I submitted the light of the 

 following easily resolved clusters to spectrum analysis. 



"4670. 2120 h. 15 M. Very bright cluster ; well resolved " *. 



"4678, 2125 h. 2 M. Bright cluster, well resolved." 



Both these clusters gave a continuous spectrum. 



I then examined the Great Nebula in the Sword-handle of Orion. The 

 results of telescopic observation on this nebula f seem to show that it is 

 suitable for observation as a crucial test of the correctness of the usually 

 received opinion that the resolution of a nebula into bright stellar points is 

 a certain and trustworthy indication that the nebula consists of discrete 

 stars after the order of those which are bright to us. Would the brighter 

 portions of the nebula adjacent to the trapezium, which have been resolved 

 into stars, present the same spectrum as the fainter and outlying portions ? 

 In the brighter parts, would the existence of closely aggregated stars be 

 revealed to us by a continuous spectrum, in addition to that of the true 

 gaseous matter ? 



The telescope and spectrum apparatus employed were those of which a 

 description was given in my paper already referred to. 



The light from the brightest parts of the nebula near the trapezium was 

 resolved by the prisms into three bright lines, in all respects similar to those 

 of the gaseous nebulae, and which are described in my former paper. 



These three lines, indicative of gaseity, appeared (when the slit of the 

 apparatus was made narrow) very sharply defined and free from nebulosity ; 

 the intervals between the lines were quite dark. 



When either of the four bright stars, a, ft, y, S Trapezii was brought 

 upon the slit, a continuous spectrum of considerable brightness, and nearly 

 linear (the cylindrical ler.s of the apparatus having been removed), was 

 seen, together with the bright lines of the nebula, which were of consider- 

 able length, corresponding to the length of the opening of the slit. The 



* The numbers and descriptions are from Sir John Herschel's Catalogue, Phil. 

 Trans. 1864, part 1. 



t " The general aspect of the less luminous and cirrous portion is simply nebulous 

 and irresolvable ; but the brighter portion immediately adjacent to the trapezium form- 

 ing the square front of the head, is shown with the 18-inch reflector broken up into 

 masses, whose mottled and curdling light evidently indicates, by a sort of granular 

 texture, its consisting of stars, and when examined under the great light of Lord Rosse's 

 reflector, or the exquisite defining power of the great achromatic at Cambridge, U. S., is 

 evidently perceived to consist of clustering stars. There can therefore be little doubt 

 as to the whole consisting of stars too minute to be discerned individually even with 

 these powerful aids, but which become visible as points of light when closely adjacent 

 in the more crowded parts . . . ." Sir John Herschel, ' Outlines of Astronomy,' 7th 

 edition, pp. 051, 652. 



