1865.] ;]^53 IChase. 



A. Single disc, or multiple and parallel discs. 

 a. Axis in magnetic meridian. 



7. When the disc was in the meridian, the currents produced a 

 slight tendency in the needle* to move in the same direction as the 

 upper part of the ring. 



8. When the disc was in the equator, the slight tendency was op- 

 posite to that in Exp. 7, and the same as if it had been produced by 

 induced electricity in the ring. 



9. When the disc was inclined to the meridian, there was a marked 

 polarity, perpendicular to the disc. 



b. Axis in magnetic equator. 



10. The disc being placed in the meridian, there was no disturbing 

 current. 



11. Placing the disc equatorially, the needle was still undisturbed. 



12. But when the disc was inclined to the meridian, the current- 

 polarity was parallel to the disc. 



c. Axis ^b° from magnetic meridian. 



13. In nearly all positions of the disc there appears to be a dispo- 

 sition in the needle to move from the axis of the ring. But when 

 the disc is in or very near the meridian, there is a slight tendency 

 towards the axis. 



In order to imitate more closely the earth's principal thermal radia- 

 tion-planes, which are all theoretically parallel with the thermal me- 

 ridians and meet at the thermal pole, I constructed a compound disc 

 (/) of two circular segments, inclined to each other at an angle of 

 about 30°, with which I tried the following experiments : 



B. Spherical-angular disc. 

 a. Axis in magnetic m.eridian. 



14. If the disc is so placed, with its opening towards the south, 

 that its angle is bisected by the meridian, the current-polarity carries 

 the needle in the same direction as the motion of the top of the ring. 



15. If the opening of the disc is turned to the north, the appara- 

 tus remaining in other respects as in the last experiment, the current- 

 polarity is reversed (as in Exp. 8). 



16. Placing the disc equatorially, I am unable to discover any 

 current-polarity. 



* In speaking of the needle's tendency, I always refer to the motion of the N. 

 pole. 



