BLECTBICITT, MAGNETISM, AND GRAVITATION. 165 



settles ; hut its dejlection is reversed, and takes place to the 



left, sr. 



On interposing a screen, it returns to zero, — and on 

 removing the obstruction, it is deflected again to the left 

 hand, 2|°. By alternately intercepting the rays, and then 

 removing the screen, a continuous vibration is maintained in 

 the new direction of 21° to 3°. 



January 23rd, llh. 30m. — Sun out, galvanometer 



deflects to the right hand 7|°. 



llh. 40m. Very bright, galvanometer deflects 



to the right hand 10°. 



llh. 53m. Sun clouded, galvanometer declines 5° . 

 p.m., 12h. 5m. Sun unclouded, galvanometer de- 

 flects to the right 9°. 



Again — 

 ** 2 0. Sun bright, galvanometer deflects to 



the left 2°. 



" 2 5. Ditto, ditto ditto 2i°. 



" 2 45. Sun obscured, ditto 0°. 



January 27th, 9 . 30. — Sun unclouded, galvanometer 5° to 

 the right hand. 



9h. 35m. Sun unclouded, galvanometer 6° to the right 

 hand. 



9h. 55m. The end of the helix is now covered entirely 

 by the shade of an iron pillar. The left side and surface of 

 the lower bundle are illuminated by the sun's rays, and the 

 needle has declined to P. 



lOh. Om., a.m. The rays now illuminate one-third of the 

 end of the helix, and the galvanometer marks 2^° to right. 

 The left side and lower bundle of the helix was now shaded 

 by a screen, and the needle speedily marked 6° to the right, 

 the helix being only half illuminated at its extremity. 



lOh. 45m. The sun is now at a considerable altitude above 

 the horizon, but the glass shade of the instrument is covered 



