160 



Mr. E. J. Stone on the Heating-Powers of [Jan. 13, 



use of a delicate reflecting astatic salvanometer, and a thermo-electric pile 

 or* nine elements. The pile was screwed into the tabe of a negative eye- 

 piece of the Greenwich Great Eqoatoreal, from which the eye-lenses had 



been removed. 



I soon convinced myself that the heat, condensed by the object-glass of 

 twelve and three -quarters inches npon my pile, was appreciable in the case 

 of several of the brighter stars ; bnt the endless changes in the zero-point 

 of the galvanometer-needle, and the magnitude of these changes, compared 

 with those arising from the heating-power of the stars, prevented me from 

 making any attempts to estimate the absolute magnitude of the effects 

 produced. Every change in the state of the sky, every formation or dis- 

 sipation of cloud, completely drove the needle to the stops. 



At the February Meeting of the Royal Astronomical Society I first 

 became aware of what Mr. Huggins had done upon this question. His 

 arrangements, however, did not appear to me to meet the difficulties which 

 I had encountered. After some trials, I arranged my apparatus as follows, 

 and with its present form I am satisfied. 



pile and galvanometer. ^ Ihe wh 

 the negative eyepieces of the grea 

 pile up in the telescope-tube. A 

 the eyepiece and terminals. The 

 the case of the pile, and is usei 

 draughts upon the case of the pile 

 the terminals of the pile to the 

 the reflecting galvanometer. Th 

 the telescope is most inconvenic 

 account of the large moving mass 



The two faces a and 3 of the p 

 current generated by any equal h« 



The telescope is first directed 

 and ,3, and allowed to remain thu 



muth. The areas 

 .'5 inch. 



e terminals of the 

 ) a tube of one of 

 mpletely shuts the 

 hen wrapped over 



The star is then placed alternately u] 

 eonesponding readings of the galvanomet 

 appears to have taken up its position, whi 



"aces a and p, and 1 

 as soon as the nee 

 f takes place in ah 



