Mr. Huggins on the Heat of the Stars. 69 



telescope to that of the refrangibility of the part of the spectrum 

 immediately about the bright liue coincident with C. 



The slit of the spectroscope was then widened sufficiently to admit 

 the form of the prominence to be seen. The spectrum then be- 

 came so impure that the prominence could not be distinguished. 



A great part of the light of the refrangibilities removed far from 

 that of C was then absorbed by a piece of deep ruby glass. The 

 prominence was then distinctly perceived, something of this form. 



A more detailed account is not now given, as I think I shall be 

 able to modify the method so as to make the outline of these objects 

 more easily visible. 



February 25. — -Captain Richards, R.N., Vice-President, in the Chair. 



The following communications were read : — 



" Note on the Heat of the Stars." By William Huggins, F.R.S. 



In the summer of 1866 it occurred to me that the heat received 

 on the earth from the stars might possibly be more easily detected 

 than the solar heat reflected from the moon. Mr. Becker (of Messrs. 

 Elliott Brothers) prepared for me several thermopiles, and a very 

 sensitive galvanometer. Towards the close of that year, and during 

 the early part of 1867, I made numerous observations on the moon, 

 and on three or four fixed stars. I succeeded in obtaining trust- 

 worthy indications of stellar heat in the case of the stars Sirius, 

 Pollux, and Regulus, though I was not able to make any quantita- 

 tive estimate of their calorific power. 



I had the intention of making these observations more complete, 

 and of extending them to other stars. I have refrained hitherto 

 from making them known ; I find, however, that I cannot hope to 

 take up these researches again for some months, and therefore ven- 

 ture to submit the observations in their present incomplete form. ; 



An astatic galvanometer was used, over the upper needle of which 

 a small concave mirror was fixed, by which the image of the flame of 

 a lamp could be thrown upon a scale placed at some distance. Usu- 

 ally, however, I preferred to observe the needle directly by means of 

 a lens so placed that the divisions on the card were magnified, and 

 could be read by the observer when at a little distance from the in- 

 strument. The sensitiveness of the instrument was made as great as 

 possible by a very careful adjustment from time to time of the mag- 

 netic power of the needles. The extreme delicacy of the instrument 

 was found to be more permanently preserved when the needles were 

 placed at right angles to the magnetic meridian during the time that 

 the instrument was not in use. The great sensitiveness of this in- 



