378 



Royal Society : — 



the green lines, the appearance of the spectra is due to a character 

 of light somewhat similar to that of a Orionis, &c, — a spectrum of 

 groups of dark lines, with spaces more or less free between them, 

 producing the effect (when the light is not sufficient to bear a slit fine 

 enough for dark lines) of a spectrum crossed by bright lines. 



The behaviour of the red line, however (of the blue one, being less 

 conspicuous, I cannot speak with so much confidence), would lead 

 to the already drawn inference that it is a real hydrogen line. 



I have examined other stars of about the same magnitude as r\ Argus ; 

 in the majority of these there is not even a suspicion of condensation 

 in any part of the spectrum ; red stars, R Leporis for instance, give a 

 spectrum not dissimilar to that of rj Argus ; but the red line on none 

 of the stars examined is so conspicuous as in rj. 



The weather since the beginning of this year has been more fa- 

 vourable, so that I am able, by degrees, to increase the amount of 

 work done. The routine work is the review of figured nebulae ; as 

 might be expected, the 4 feet gives views considerably different from 

 the C. G. H. drawings ; but at present I have nothing worthy of spe- 

 cial mention. 



The light of the nebulse, as they are taken up for general exami- 

 nation, is analyzed with the prism ; of those which have been exa- 

 mined I have yet found none of which it may be certainly said that 

 the light is not of definite refrangibilities. 



In irregular nebulse, the bright knots even, which are so distinctly 

 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 clus- 

 ters as 47 Toucan, I cannot speak with certainty ; but if the light were 

 monochromatic, 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 cata- 

 logue) of which I enclose a diagram 

 from measured positions ? The confi- 

 guration differs so widely from that 

 given in the Philosophical Transac- » 



tions, that, with reference to the ro- 

 tation of the two nebulous stars, it 

 would be interesting to have the evi- •$ 

 dence of any additional observations 

 made at Parsonstown. 



From Mr. Muggins's observations 

 of the nebulas 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, pro- 

 bably G. I have not specially ex- 



N 



