LECTRO-MAGNETIC EXPERIMENTS AND OBSERVATIONS. 477 



veloped an effect on the needle when the zinc was west, or east, 

 which could not be detected by using a small connecting 

 wire. 



On comparing the results obtained by using different kinds 

 of connecting pieces, it appears, that if the needle be applied 

 along their exterior surface, as in the 

 direction S, o, N, the deflection will 

 be the same, while the relative posi- 

 tion of the zinc and copper are un- 

 changed, or while the electro-motive <> 

 current flows in one direction ; and 

 if the needle be carried along the 

 interior surfaces of the connecting piece, as in the direc- 

 tion 5, i t ra, the deflection will be uniformly in the opposite di- 

 rection. 



The thin brass cylinder Fig. 4. was then applied to the tray 

 and plate apparatus, Fig. 7. 



I. Zinc North. 



1. Needle in its axis, deflected E. 



2. - at its upper surface E. 



3. - at its lower surface W. 



II. Zinc South. 



1. Needle in its axis, not at all deflected. 



2. - above, deflected W. 



3. - below - E. 



III. Zinc West. 



1. Needle in its axis not deflected, but vigorously acted on. 



2. - above, not visibly acted on. 



3. - below, had its poles inverted. 



Zinc 



