1870.] 



Great Melbourne Telescope. 



19 



mottled as to point to a cluster condition, give out, as far as I have yet seen, 

 light which is monochromatic, or nearly so. 



Acknowledged clusters, where discrete stars are plainly discernible, are 

 of course excluded ; of the nebulosity mixed up with such clusters as 

 4 7 Toucan, I cannot speak with certainty ; but if the light were monochro- 

 matic, I think that (in the case particularized at least) the brilliancy would 

 be sufficient to afford a definite impression. 



Would you call Lord Rosse's attention to 1477-78 (general catalogue), 

 of which I enclose a diagram from 

 measured positions ? The configura- 

 tion differs so widely from that given 

 in the Philosophical Transactions, 

 that, with reference to the rotation 

 of the two nebulous stars, it would 

 be interesting to have the evidence 

 of any additional observations made 

 at Parsonstown. F 



From Mr. Huggins's observations 

 of the nebulse in Orion, I gather 

 that he has seen only the three usual 

 lines ; with a wide slit, I had lately 

 a very strong suspicion of a fourth 

 line, probably G. I have not spe- 

 cially examined the nebulse since; 

 but probably Mr. Huggins will be able to give confirmatory evidence. 



On the night of February 1 st we had a pretty brilliant auroral display ; 

 being at work at the time, I missed part of it ; but as soon as I became 

 aware of its existence I applied the spectroscope. At moments four lines 

 already known were easily visible, the chief line being remarkably brilliant. 

 A much narrower slit than that used could have been borne at the time of 

 maximum display, which, however, lasted only a few moments. I was 

 intent on measuring the lines, as at the time I had no published definite 

 information with reference to other than Angstrom's special line ; but at 

 moments light was seen at the red end of the spectrum sufficiently bright 

 to leave a distinct impression of colour ; when, however, special attention 

 was devoted to that part of the spectrum the aurora had greatly diminished 

 in brilliancy, so that I was unable to make out whether a red line existed, 

 or whether there was a general spectrum at the red end. I incline to the 

 latter opinion, and put it down to the rose-coloured arc ; this arc, however, 

 which seemed pretty brilliant after the streamers had disappeared, did not 

 then give a visible spectrum. Probably this phenomenon has been ob- 

 served before to better purpose ; but I cannot find mention thereof in 

 published accounts. Yours truly, 



A. Le Sueur. 



c 2 



