470 ELECTRO-MAGXETIC EXPERIMENTS AND OBSERVATIONS. 



zinc and copper plates, depends rather on the direction which 

 is thus communicated to the electro-motive currents, than on 

 the point of the compass from which they begin to flow. 



Helices were substituted for the connecting wires already 

 described. These were usually formed by bending copper- 

 wire 10 or 12 times round a wooden cylinder. We did not find 

 any difference in effect, whatever might be the metal of which 

 they were made, or whether they were ^, 1, 2, 3, or 4 inches 

 in diameter j but we found those of two inches most con- 

 venient in our experiments. They were either right or left 

 helices ; and for one experiment we employed a helix, one- 

 half of which was a right, and the other a left helix *. 



In the following experiments, the needle was generally in- 

 troduced iu the centre of the helix ; but it did not alter the re- 

 sults, when moved about in it, provided the needle had free 

 space to turn round. 



Experiments with a Right Helix. Fig. 5. 



1. Zinc North. 



Needle introduced in the axes had its poles inverted. 



2. Zinc South. 



No deflection of the needle. 



3. Zinc West. 



Needle deflected to the E. 



4. Zinc East. 



Needle deflected to the W. 



Experiments 



* Those unaccustomed to such operations, find some difficulty in distinguish-'] 

 iiig between a right and a left helix ; but if it be placed on one end, the spires of 

 a right helix rise in the direction of the sun's diurnal course ; those of a left helix 

 in the opposite direction. 



