246 



VOLTAIC ELECTRICITY. 



other light under human control, the temperature 

 of which is unequalled &T/ any other artificial source 

 of heat. 



39O. Deflection of the Magnetic Needle. 



The Voltaic current has a marked effect in the deflection 

 | of the magnetic needle, and tends to 

 place the needle at right angles to 

 the direction of the current. This 

 may be easily shown by Oersted's 

 apparatus represented in Fig. 191. 

 It consists of a magnetic needle and 

 a brass wire frame with three pole- 

 FIG. 191. cups, permitting the current to be 



passed over, under, or around the magnet. 



(a.) If tlie current pass above the needle from north to south, the 

 end of the magnet ( 317) will be deflected toward the east ; 

 if it pass from south to north, the end of the needle will be 

 deflected toward the west. If the current pass below the needle, 

 the deflections will be the opposite of those just mentioned. 



S91. The Galvanometer. The galvanometer de- 

 pends upon the principles set forth in 

 the last article. It is a very delicate 

 piece of apparatus for detecting 

 the presence of an electric current 

 and determining its direction and 

 intensity. In Oersted's apparatus the 

 needle is heavy, and a considerable 

 force is needed to set it in motion ; 

 in the galvanometer the needle is very 

 light, and is easily set in motion. 

 In Oersted's apparatus the needle is 

 held in the magnetic meridian by the directive influence 



