ELECTRO-MAGNETIC EXPERIMENTS AND OBSERVATIONS. 473 



the supposed current, passing from the zinc toward the copper 

 by the helices. 



With right helices, the needle as invariably arranges itself in 

 the direction of the axis of the helix ; but, in this case, the 

 south pole of the needle is always directed, so as to meet the 

 current, which we have supposed to proceed from the zinc to 

 the copper by the connecting wires. 



This general statement will supersede the necessity of de- 

 tailing the numerous experiments which we made to deter- 

 mine these laws. It is evident that the deflections of the 

 needle, when the helices were arranged either in an east or a 

 west direction, could never be less than 90° ^ and in certain 

 directions must have amounted to complete inversion of tlie 

 poles. 



The foregoing experiments were made with horizontal heli- 

 ces ; and we conceived that it was important to ascertain the 

 effect which an inclined, or a vertical position of the helices 

 might produce on the needle. 



With a vertical helix, as in Fig. 7., a needle, poised on a 

 centre, dipped so much as to have its free motion destroyed : 

 we therefore introduced a magnetic needle, suspended by a 

 fine thread, or a fibre of raw silk. This uniformly assumed 

 the direction of the axis of the helix, whether truly vertical, or 

 inclined to the horizon. 



In a Right Vertical Helix. 



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

 permost, the N. pole is depressed, 



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

 most, the N. pole is elevated. 



That is, the south pole, as in a horizontal right helix, is 

 turned, to meet the supposed current proceeding from the 

 zinc. 



3 o 2 In 



