Electro-Magnetic Apparatus and Experiments, 263 
tion. m, is the electro-magnet. a, the armature of soft iron. 
is an.upright stem of brass, to receive and make the bourition of : 
the shaft of the armature. , is a disc of wood-or ivory to brace 
the upright ‘stem e. -¢, is oné termination-of the magnet. coil,- 
Serving as‘a conducting spring. d, is the other conducting spring 
passing through. the fia b, into the cup 2, for battery connexion. 
The other termination of the magnet wires passes into the cup p. 
At c, d, firmly fixed to the shaft, is a cylindrical piece of silver, 
which may: be. technically called the cut-off, or electrotome. 
The spring c, plays upon the whole portion of the cut-off. “The 
spring d, plays upon the dissected part, whose metallic ibislone 
are so arranged that they shall come into contact with the spring 
d, when the armature is a little inclined from right angles to the 
plane of the magnet, and leave spring.d, before the armature ar- 
rives at equilibrium. This armature revolves much faster than 
would a magnet changing its poles. “Besides the advantage of 
greater simplicity, the revolving armature. possesses advantages 
which cannot be gained by change of poles, or by revolving 
magnets, where the power is only cut off without a change of 
poles. Suppose another electro-magnet to be placed at right an- 
gles to the magnet m, in the figure, and the cut-off so arranged 
that the two magnets shall be charged in succession by the revo- 
lution of the armature. The velocity of the armature will thus 
be nearly doubled without the addition of more battery, for the 
points of action are doubled, and’ only one magnet charged at a 
time. _ This same plan admits of enlargement‘on any scale, only 
with the alteration of the mode of revolution. If electro-mag- 
netism should ever be introduced for smatl powers, such as turn- 
ing lathes, &e. it probably will be effected by — the See 
or vibrating armature machines. 
si ‘Reciprocating Armature Engine. 
Figure 6, represents an electro-magnetic engine with vibrating 
or reciprocating armatures. a, a, are the electro-magnets, firmly 
secured to the base board and the wooden table ¢. 5, b, are the 
armatures of soft iron connected with the shaft (¢) by stout brass 
arms. The balance beam, connecting rods, and balance wheel, 
represented in the figure, require no particular description. The 
cut-off by which the magnets are alternately charged, is on the 
shaft of the balance wheel at m. It is simple in construction, 
