ELECTRO-MAGNETIC EXPERIMENTS AND OBSERVATIONS. 471 



Experiments with a Left Helix. Fig. 6. 



1. Zinc North. 



Needle not deflected. 



2. Zinc South. 



Needle had its poles inverted. 



3. Zinc West. 



Needle deflected to W. 



4. Zinc East. 



Needle deflected to E. 



Experiments with a Double Helix. 



This helix is 6 inches in length, and 2 in diameter; it con- 

 sists of 16 spires, 8 of which are in a right, and 8 in a left di- 

 rection. 



The needle, when placed in either end, was deflected, as in 

 the order of the simple helices, to which it belonged. When 

 placed in the centre of this helix, the needle only obeyed ter- 

 restrial magnetism ; but the slightest deviation to either extre- 

 mity produced a deflection. 



Instead of the helices, we employed a thin tube of brass, 

 Fig. 4. ; but with the small apparatus no certain effects were 

 produced. In subsequent experiments, however, with a larger 

 galvanic arrangement, we remarked singular irregular motions 

 of the needle in its axis, which were not easily reducible to 

 any general law. 



To increase the power of our electro-motive apparatus, 

 without rendering it complicated, seemed desirable, as we 

 thought that we perceived a law, respecting the action of he- 

 lices, which we hoped to develope more clearly by an increase 

 of power. 



We procured a copper tray, 14 inches long by 10 inches 

 wide, and 1 deep, A A, Fig. 7. BB is a plate of zinc, 13 



vol. ix. p. ii. 3 o inches 



