242 AN>'DAL OF SCIENTIFIC DISCOVERY. ^ 



spcftrnm of nitrogen directly witli 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 whieh are peeuliar to nitrogen. 

 It may be, tiierefore, that the occurrence of this one line only 

 indicates a form of matter more elementary than nitrogen, and 

 which our analysis has not jet cnal)lcd us to detect. 



" In a similar manner, tlie faintest of the lines was found to 

 coincide ^\ ith the green line of hydrogen. 



"Tlie mitldle line of the tluve 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, l)ut it does not coincide with it. Besides tiiese 

 bright lines, there was also an exceedingly faint continuous spec- 

 trum. The si)ectrum had no apparent In-eadth, and must there- 

 fore have been formed liy a uiiuiiti^ point of light. The pr)sition 

 of tiiis faint spectrum, wliich crossed the bright lines ai)out tiie 

 middle of their length, showed that the briglit point producing it 

 was situated about the centre of the nebula. Now this nebula 

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

 servation that tile matter of tiie nucleus is almost certainly not in 

 a state of gas, as is the material of the surrounding nel)ula. It 

 consists of opaque matter, whicii may exist in the form of an in- 

 candescent fog of soliil or liquid particles. 



*' The new and unexpcctetl 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 

 nei)ul;e give similar spectra? Especially it was of importance to 

 ascertain whether those nei)ula3, which the telescope had certainly 

 resolved into a close aggregation of bright points, would give a 

 spectrum indicating gascit}'. 



" The observation with the prism of these objects is extremely 

 dillicult. on account of their great faintness. Besides this, it is 

 only when the sky is very clear, and the moon is absent, that the 

 prismatic arrangement of their light is even possible. During 

 the last two 3'ears, I have examined the spectra of more than 

 sixty nebuUe and clusters. These may be divided into two great 

 groups. One group consists of the nebulae which give a spec- 

 trum similar to the one I have already described, or else of one or 

 two only of the tin-ee bright lines. Of the six objects examined, 

 about oue-tliird Ijelong to the class of gaseous bodies. The liglit 

 from the remaining forty nebulae and clusters becomes sjiread out 

 by the prism into a spectrum which is apparently continuous. 



"The most remarkable, and possibly the nearest to our system, 

 of the nebulae presenting a ring formation, is the well-known 

 Annular Nebula in Lyra. The spectrum consists of one bright 

 line only. When the slit of the instrument crosses the nebula, 

 the line consists of two brighter portions corresponding to the 

 sections of the ring'. A much fainter line joins them, which shows 

 that the faint central portion of the nebula has a similar constitu- 

 tion. 



" A nebula remarkaVde for its large extent and peculiar form, 

 is that known "as the Diunb-bell Nebula. The spectrum of this 



