162 



ON THE IDENTITY OF LIGHT, HEAT, 



galvanometer maiks 5°, with no wire of connexion between 

 the mercury cups. By completing the circuit, no change ; 

 in two minutes the indicator marks 4°. Removed the 

 connecting wire, and the galvanometer remains as before, 

 at 4°. 



I now interposed a screen. In ^ min. the needle receded 

 to Oj° ; in 1^ m., quite to zero. Removed the screen at 

 11 .20 a.m., and in 1 m. galvanometer 2^°-, in Ik m., 4|° ; 

 in If m., 5'^; in 2 m., the sun now unclouded, 6°. Circuit 

 incomplete. 



Removed the mercury cup into which the south wire 

 was inserted — the only one illuminated by the solar rays. 

 The sun being quite unclouded, the needle indicated lO*^. 

 I again interposed the screen, and the needle returned to 

 2^°. Fearing lest the galvanometer had been altered, as 

 the indication was so high, I removed zero to where the 

 needle became stationary at 2^°; and on taking away the 

 screen, in 1 m. the needle indicated 7^^°, and afterwards 8°^. 

 At llh. 35m., the needle deflected to 9°. The mercu- 

 rialized end of the galvanometer wire was now enclosed in 

 paper, to ensure that there should be no supposed thermo- 

 electric action by heating copper in communication with 

 mercury; but the galvanometer remained just as before. 



There was no alteration in the results obtained by plunging 

 a wire, in connection with the north end or terminal of the 

 galvanometer, into cold water. 



The sun's rays are beginning to fall upon and illuminate 

 the north extremity of the helix, and the needle gradually 

 declines. 



.January 3rd, 1851. — All the following deflections were to 

 the right hand: — 



a.m., llh. 30m. Sun somewhat clouded, galvanometer 2°. 

 " 11 . 45. " brighter, " 2i°, 



" 11. 50. " still brighter, " 6^ 



p.m., 4 . 55. " bright; the galvanometer now indi- 

 cates 8°. 



