474 ELECTRO MAGNETIC EXPERIMENTS AND OBSERVATIONS. 



In a Left Vertical Helix. 



1. When the end of the helix connected with the zinc is up- 

 permost, the N. pole of the needle is elevated. 



2. When the end of the helix connected with the zinc is low- 

 ermost, the N. pole of the needle is depressed. 



That is, the north pole, as in a left horizontal helix, is 

 turned, to meet the current proceeding from the zinc. 



Similar experiments were made on helices inclined at angles 

 of 70° and 20°. The needles assumed the direction of tne axis 

 of those helices ; and the other phenomena were similar to 

 what are above stated. 



We may then reduce the influence of the interior of the he- 

 lices on electro-magnetic arrangements, into two general laws. 



1st, When a magnetic needle is introduced into such a he- 

 lix, it has a tendency to assume a direction parallel to the axis 

 of the helix. 



2d, When the helix is a right helix, the South pole of the 

 needle is deflected 'toward that part of it in connection with 

 the zinc ; and when it is a left helix, the North pole of the 

 needle is deflected toward that part of it in immediate contact 

 with the zinc. 



In prosecuting our experiments, we had occasion to observe, 

 that the upright wires supporting the helices, were not with- 

 out their influence on the needle. When the needle approach- 

 ed the vertical portion of the connecting wires, there were 

 marks of strong electro-magnetic action ; but the deflections of 

 the needle differed at each side of the wire. There is some 

 difficulty in ascertaining the precise effects of each side of the 

 wire, and we therefore substituted, first, a rectangular tube of 

 copper, of the same form as the connecting wire in Fig. 2., the 

 sides of which were about f ths of an inch in breadth ; and after- 

 wards a solid piece of lead, cast of the same size and shape as 



the 



