Mr. Hug-gins on the Heat of the Stars. 71 



produce a deviation of the needle greater than was to he expected 

 from the stars. 



The apparatus was fixed to the telescope so that the surface of the 

 thermopile would he at the focal point of the object-glass. The 

 apparatus was allowed to remain attached to the telescope for hours, 

 or sometimes for days, the wires being in connexion with the galvano- 

 meter, until the heat had become uniformly distributed within the 

 apparatus containing the pile, and the needle remained at zero, or 

 was steadily deflected to the extent of a degree or two from zero. 



When observations were to be made, the shutter of the dome was 

 opened, and the telescope, by means of the finder, was directed to a 

 part of the sky near the star to be examined where there were no 

 bright stars. In this state of things the needle was watched, and 

 if in four or five minutes no deviation of the needle had taken place, 

 then by means of the finder the telescope was moved the small dis- 

 tance necessary to bring the image of the star exactly upon the face 

 of the pile, which could be ascertained by the position of the star as 

 seen in the finder. The image of the star was kept upon the small 

 pile by means of the clock-motion attached to the telescope. The 

 needle was then watched during five minutes or longer ; almost always 

 the needle began to move as soon as the image of the star fell upon 

 it. The telescope was then moved, so as to direct it again to the sky 

 near the star. Generally in one or two minutes the needle began 

 to return towards its original position. 



In a similar manner twelve to twenty observations of the same star 

 were made. These observations were repeated on other nights. 



The mean of a number of observations of Sirius, which did not 

 differ greatly from each other, gives a deflection of the needle of 2°. 



The observations of Pollux 1|°. 



No effect was produced on the needle by Castor. 



Regulus gave a deflection of 3°. 



In one observation Arcturus deflected the needle 3° in 15 minutes. 



The observations of the full moon were not accordant. On one 

 night a sensible effect was shown by the needle ; but at another time 

 the indications of heat were excessively small, and not sufficiently 

 uniform to be trustworthy. 



It should be stated that several times anomalous indications were 

 observed, which were not traced to the disturbing cause. 



The results are not strictly comparable, as it is not certain that 

 the sensitiveness of the galvanometer was exactly the same in all the 

 observations, still it was probably not greatly different. 



Observations of the heat of the stars, if strictly comparable, might 

 be of value, in connexion with the spectra of their light, to help us 

 to determine the condition of the matter from which the light was 

 emitted in different stars. 



I hope at a future time to resume this inquiry with a larger tele- 

 scope, and to obtain some approximate value of the quantity of heat 

 received at the earth from the brighter stars. 



"On the Fracture of Brittle and Viscous Solids by * Shearing.'" 

 By Sir William Thomson, F.R.S. 



On recently visiting Mr. Kirkaldy's testing works, the Grove, 



