1865.] Physic*. 217 



view, the light of two easily-resolved clusters was submitted to 

 spectrum-analysis, but both gave a continuous spectrum. 



Mr. Huggins then examined the Great Nebula in the Sword- 

 handle of Orion.* The results of telescopic observation on this nebula 

 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 has already been given in our Chronicles of 

 Astronomy. When turned towards the brightest parts of the nebula 

 near the trapezium, the light was resolved by the prisms into three 

 bright lines in all respects similar to those of the gaseous nebulae. 

 These three lines 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 /3, y, 5, Trapezii, was brought upon the slit, a continuous 

 spectrum of considerable brightness, and nearly linear (the cylindrical 

 lens of the apparatus having been removed), was seen, together with 

 the bright lines of the nebula, which were of considerable length, 

 corresponding to the length of the opening of the slit. The fifth 

 star y', and the sixth a.', are seen in the telescope, but the spectra of 

 these are too faint for observation. 



The positions in the spectra of a , ft, y, §, Trapezii, which corre- 

 spond to the positions in the spectrum of the three bright lines of 

 the nebula, were carefully examined ; but in no one of them were dark 

 lines of absorption detected. 



The part of the continuous spectra of the stars a, yS, y, near the 

 position in the spectrum of the brightest of the bright lines of the 

 nebula, appeared on a simultaneous comparison to be more brilliant 

 than the line of the nebula ; but in the case of y, the difference in 

 brightness was not great. The corresponding part of § was perhaps 

 fainter. In consequence of this small difference of brilliancy, the 

 bright lines of the adjacent nebula appeared to cross the continuous 

 spectra of y and o Trapezii. 



Other portions of the nebula were then brought successively upon 

 the slit ; but throughout the whole of those portions of the nebula 

 which are sufficiently bright for this method of observation the spec- 

 trum remained unchanged, and consisted of the three bright lines only. 

 The whole of this great nebula emits light, which is therefore identical 

 in its characters ; the light from one part differs from the light of an- 

 other in intensity alone. The clustering stars, of which, according to 



* 'Proceedings of the Royal Society,' vol. xiv. p. 39. 



z 2 



