306 Lieut. Herschel's Observations of Southern Nebulce. [Feb. 25, 



spectroscope. The position of the line has not been mea- 

 sured. 



No. 1565. " A planetary nebula ; pretty bright ; pretty small ; extremely 

 little extended; barely resolvable." The " linear" cha- 

 racter of the spectrum of this object has been already re- 

 cognized ; but it was again examined, as a test of the ad- 

 vantage of removing the slit. It is a considerably larger 

 and less bright object than No. 1225, and situated in a 

 magnificent cluster of stellar points. In the open field of 

 the spectroscope it appeared as a similar faint patch of light, 

 in the midst of an infinity of streaks. Nothing could have 

 been more conclusive as a test. 

 No. 1185. "Remarkable; very bright; very large; round; with tail ; 



much brighter in middle, a star of 8'9 magnitude." A 

 neighbour of the great nebula of Orion. Examined with 

 the slit repeatedly. On the first occasion the spectrum was 

 described as "linear, but faintly seen ; not certainly seen in 

 presence of the central star. When the latter is put out, 

 the spectrum becomes broadly continuous, with monochro- 

 matic light across it." On the next it was, "To-night I 

 could trace no lines. There is ample light, but it is not 

 1 linear,' though certainly confined principally to the neigh- 

 bourhood of the position of the ordinary lines. The spec- 

 trum in any case occupies nearly the width of the field, and 

 is not much less in length." On a third occasion I noted 

 that I could " barely trace any lines, while there is a broad 

 patch of spectral light on either side, which is certainly not 

 due to the stellar centre." The trace of lines is confirmed 

 on a fourth occasion. 

 I think I am justified in saying that we have here a nebula of a class 

 or description intermediate between those wliich show a clear continuous 

 spectrum only, and those which show bright lines only. Not that the ap- 

 parent character of these two extremes is necessarily absolute ; it is far 

 more probable that the non-appearance in either, of the distinguishing 

 characteristic of the other, is relative only. Indeed there are not wanting 

 instances of nebulas whose place in a series would be short of the latter 

 extreme. For instance, — 

 No. 826, supra, and 



No. 4964. "Extremely remarkable; a planetary nebula; very bright; 



pretty small ; round ; blue." Presented " a continuous 

 spectrum and a fourth line (besides the three usual ones) ; 

 the first strongly suspected, the last less so." The fourth 

 line I find has been noted by Mr. Huggins. 

 And the great nebula of Orion appears to be of the same order. I have 



examined this nebula repeatedly of late, because on the first occasion of 



