168 



ON THE IDENTITY OF LIGHT, HEAT, 



of the helix produces an action completely antagonistic to 

 that of the sun's action upon its southern extremity. Thus 

 on June 27th, 1850, the opening in the dial card having been 

 enlarged, the needle deflected to 10° ; exposed the upper 

 bundles of the helix to the sun's rays, the needle returned 

 to 7J°, and vibrated continually at this point. Shaded the 

 dial opening, and the needle deflected to 10°, and after- 

 wards 11°. This experiment was performed several times 

 and attended with similar results. By shading the extre- 

 mity of the helix and exposing its upper surface only, needle 

 reversed 3° to the right hand. 



The powers of reflected light were tried by reflecting the 

 solar rays upon various portions of the helix, and this in a 

 variety of directions, but without any change occurring in the 

 position of the needle. 



I also verified the experiments of 1850-51, by similar 

 experiments in 1851-52, at like periods of the year, but 

 invariably with the same kind of deflection, and in the 

 same direction corresponding with the altitude of the sun 

 above the horizon. 



Thus September 10th, 1851, Ih. 30m., deflection to the left 

 hand, 3°. 



At 3h. 45m. The northern extremity of the helix was alone 

 illuminated, but no deflection of the needle could be obtained. 

 The same results occurred also in October, and November — 

 deflection 5° to the left. 



The Vibratory Period, 1852. 



1852, January 23rd, 12^ p.m. — Deflection to the right hand, 

 as in the previous year at this date, and the needle returned 

 to zero on obstructing the rays. 



January 30tl), 12 noon. — Galvanometer deflects to the 

 right hand, the sun becomes obscured, and the needle 

 returns. 



February 12th, lOh. 40m.— Needle deflects 3° to the left 



