204 LECTUEE ON THE EESULTS OF SPECTEUM ANALYSIS 



The interest connected witli an answer to this question has much increased 

 since Sir William Herschel suggested that these objects are portions of the pri- 

 mordial material out of which the existing stars have been fashioned ; and further, 

 that in these objects we may study some of the stages through which the suns 

 and planets pass in their development from luminous cloud. 



The telescope has failed to give any certain information of the nature of the 

 nebulse. It is true that each successive increase of aperture has resolved more 

 of these objects into bright points, but at the pame time other fainter nebulae 

 have been brought into view, and fantastic wisps and diffused patches of light 

 have been seen, which the mind almost refuses to believe can be due to the 

 united glare of innumerable suns still more remote. 



Spectrum analysis, if it could be successfully applied to objects so excessively 

 faint, was obviously a method of investigation specially suitable for determining 

 whether any essential physical distinction separates the nebulse from the stars. 



I selected for the first attempt, in" August, 18G4, one of the class of small but. 

 comparatively bright nebulse. My surprise was very great on looking into the 

 small telescope of the spectrum apparatus to perceive that there was no appear- 

 ance of a band of colored light, such as a star would give, but in place of this 

 there were three isolated bright lines only. 



This observation was sufficient to solve the long agitated inquiry in reference 

 to this object at least, and to show that it was not a group of stars, but a true 

 nebula. 



A spectrum of this character, so far as our knowledge at present extends, can 

 be produced only by light which has emanated from matter in the state of gas. 

 The light of this nebula, therefore, was not emitted from incandescent solid or 

 liquid matter, as is the light of the sun and stars, but from glotmng or luminous 

 gas. 



It was of importance to learn, if possible, from the position of these bright 

 lines, the chemical nature of the gas or gases of which this nebula consists. 



Measures taken by the micrometer of the most brilliant of the bright lines 

 showed that this line occurs in the spectrum very nearly in the position of the 

 brightest of the lines in the spectrum of nitrogen. The experiment was then 

 made of comparing the spectrum of nitrogen directly with the bright lines of 

 the nebula I found that the brightest of the lines of the nebula coincided with 

 the strongest of the group of lines which are peculiar to nitrogen. It may 

 be, therefore, that the occurrence of this one line only indicates a form of matter 

 more elementary than nitrogen, and which our analysis has not yet enabled us 

 to detect. 



In a similar manner the faintest of the lines was found to coincide with the 

 green line of hydrogen. 



The middle line of the three lines which form the spectrum of the nebula does 

 not coincide with any strong line in the spectra of about thirty of the terrestrial 

 elements. It is not far from the line of barium, but it does not coincide with 

 it. Besides these bright lines, there was also an exceedingly faint continuous 

 spectrum. The spectrum had no apparent breadth, and must, therefore, have 

 been formed by a minute point of light.' The position of this faint spectrum, 

 which crossed the bright lines about the middle of their length, showed that the 

 bright point producing it was situated about the centre of the nebula. Now 

 this nebula possesses a minute but bright nucleus. We learn from this obser- 

 vation that the matter of the nucleus is almost certainly not in a state of gas, as 

 is the material of the surrounding nebula. It consists of opaque matter, Avhich 

 may exist in the form of an incandescent fog of solid or liquid particles. 



The new and unexpected results arrived at by the prismatic examination of 

 this nebula showed the importance of examining as many as possible of these 

 remarkable bodies. Would all the nebulae give similar spectra ? Especially it 

 was of importance to ascertain whether those nebulae which the telescope had 



