60 



List of Nebula and Clusters observed at Bangalore, [Recess, 



The evidence in the case of these is purely negative. They have been 

 brought on the slit with sufficient precision to make it in each case almost 

 a certainty, taking into consideration their apparent brightness, that had 

 their light been monochromatic in the sense in which other similar nebula 

 are so, it must have been recognized as such ; whereas, if dispersed, ana- 

 logy would forbid any expectation of detecting the feeble continuous spec- 

 trum. In each case I have satisfied myself that the inference was a legi- 

 mate one before recording it, both by testing the focal adjustment on a 

 neighbouring star and by repeating (if necessary) the adjustment in respect 

 of direction, until the case appeared a hopeless one. 



Some instances, in which the presumption was not so strong as to seem 

 to justify the inference, are omitted from this list. 



Several nebulte, the measurements of whose spectra were given in my 

 previous list, were reexamined. I am rather inclined to believe that the 

 position of the principal light is not quite constant for all. The newer 

 and more careful measurements certainly throw doubts upon some of the 

 earlier ones. Nevertheless I have reason to believe that the discordances 

 are not wholly due -to inaccurate determination. But on this and other 

 points I hope to be able to write more fully on a future occasion, when a 

 larger number have been remeasured. The following were reexamined. 

 No. 4066. Yery bright spectrum ; 3 lines certainly ; faint continuous spec- 

 trum suspected. 



No. 4510. Very bright spectrum ; 2 lines only seen, both hazy; compa- 

 ratively distinct continuous spectrum of some length on both 

 sides of the principal line. 



No. 4390. Seen easily in a bright field ; 3rd line seen certainly. 



No. 436 1 . Yery large ; 2 lines only ; ill defined ; decided continuous spec- 

 trum at the brightest point {not stellar). 



P.S. — I have throughout used the word "monochromatic" in prefer- 

 ence to "linear" intentionally, because, though not strictly correct, it ap- 

 pears more so than the latter. Unless a cylindrical lens is used, or un- 

 less the object examined is so great as to be partially stopped out by the slit 

 (generally a very wide one), the term "linear" seems purely conventional. 

 I have reason to believe that some of my earlier measures were erroneous, 

 partly through not realizing the " play," so to speak, of the small image 

 within a wide slit, the linear character being illusory. The term has be- 

 come so intimately associated with spectral appearances, that one is apt to 

 forget how completely mechanical, and therefore conventional a character- 

 istic of the quality of light is expressed by it. Thus I find that, in more 

 than one instance, expectation is entertained of possible bright "lines" 

 being seen during the coming eclipse, without the intervention of a slit, as 

 though this were an inherent quality in light itself. 



