164! ON THE IDENTITY OF LIGHT, SEAT, 



The motions of the galvanometer appear much more rapid 

 since the blackening of the extremity of the helix, 

 p.m., 12h. 45m. The sun is now out again, the gal- 

 vanometer deflects to 4°, then 5°, 



The rays obstructed by a cloud, it declines to ... P. 



The sun becoming brighter, 6°; now 7°. 



Obscured still by thin clouds, and no prospect of 



being clearer 7°. 



N.B. Up to this period the deflections had been from the 

 12th December all to the right hand. 



The Vibratory Period. 

 Effects of Shade — Deflection changed. 



January 22nd, 1851, a.m., 9h. 45m. — Half the helix shaded 

 by a pillar, galvanometer 4° to the right hand. Two-thirds 

 shaded, galvanometer 2i°. The shade still encroaching, the 

 galvanometer gradually declines. Now 3 wires only un- 

 shaded, galvanometer 2°, and at length zero. 



llh. 45m. The sun is now brightly shining upon the whole 

 extremity of the helix and all along the lower bundle of 

 wires, and the galvanometer remains at zero. 



A piece of sheet copper was now interposed as a screen to , 

 shade the lower bundle of wires of the helix, and permit 

 the rays to illuminate only its extremity — galvanometer 

 deflected to 7i°. 



It will be observed that it was the 22nd of January, at 

 mid-day, and the sun had ascended a consi'derable altitude 

 above the horizon. The influence hitherto exerted on the 

 galvanometer appeared destroyed. Sometimes it would diverge 

 in one direction, and sometimes in the opposite. Vibratory 

 movements began again to make their appearance as they 

 had done on the 14th of November, 1850; at which period, 

 and for some time afterwards, the deflections of the needle 

 were towards the left hand. By and bye, the galvanometer 



