ioo AMPERE'S FLOATING HELIX COIL. 



steadily to the N and s poles of the artificial globe ; 

 and faithfully continues to point to them in 

 whatever direction it may be turned. 



To increase the intensity of the electric currents, 

 Ampere multiplied the number of circuits, by 



winding the conducting 

 wire in a spiral; Fig. 23. 

 This simple apparatus 

 develops all the charac- 

 teristic functions of a 

 magnetic needle mount- 

 23 . ed on a pivot. One par- 



ticular end always turns toward the north pole 

 of the earth, and when disturbed returns to that 

 direction. This coil serves to represent the trans- 

 verse position of the magnetic needle mounted on 

 the little globe; w represents the cross-section 

 or end of a conducting wire transmitting a current 

 in a direction from east to west, corresponding 

 with the direction of the terrestrial currents. The 

 battery current through w, being more immediately 

 powerful than the terrestrial electric current, in 

 whatever direction the conducting wire w may be 

 turned in relation to the cardinal points, the float- 

 ing coil will turn and become arranged with its 

 underside currents moving in the same direction as 

 the current in w ; and will always remain stationary 

 in a position crosswise to the current through w. 



If the wire w be held above the spiral coil, 

 where the circling current is in an opposite direc- 



