Eilectro-Magnetic Apparatus and Experiments. 267 
at the break pieces are brighter. Tn all cases where motion is 
duced by the galvanic ¢ it, 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 Armature. 
Figure 7, represents a vibrating armature, to be used as an 
electrotome, in connexion with an apparatus: affording sparks ¢ or 
shocks. 6, is a small electro-magnet, (of the actual size given in 
Figure 7. 
ANG, 
a 
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 
ds used. a, aslender iron wire for an armature, suspended on a 
delicate shaft. 0, is a connecting wire of eopper fixed to one end 
of the armature, joining the mercury in the two cups d and e. 
and n, 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 
€, is of glass, or very thin ivory, to exhibit the illumination from 
