Electro-Magnetic Apparatus andr Experime7its. 267 



at the break pieces are brighter. In all cases where motion is pro- 

 dnced by the galvanic current, it must meet with considerable re- 

 sistance, either from secondary" currents or from the breaks in the 

 circuit. The compound current probably has a greater velocity 

 than an elementary current, and meets with less resistance from 

 opposing secondaries and passing breaks. 



Vibrating At'mature. 



Figure 7, represents a vibrating armature, to be used as an 

 electrotome, in connexion with an apparatus affording sparks or 

 shocks, b, is a small electro-magnet, (of the actual size given iu 



the figure,) and covered with only a single coil of wire, so as not 

 to detract much from the power of the instrument with which it 

 is used, a, a slender iron wire for an armature, suspended on a 

 delicate shaft, o, is a connecting wire of copper fixed to one end 

 of the armature, joining the mercury in the two cups d and c. p 

 and w, are the terminal cups for connexions. The connexions 

 between the cups and the ends of the magnet wire, are made 

 under the base board, and marked by the dotted lines. The cup 

 c, is of glass, or very thin ivory, to exhibit the illumination from 



