Electro-Magnetic Apparatus and Experiments. 263 



tion. m, is the electro-magnet, a, the armature of soft iron, e, 

 is an upright stem of brass, to receive and make the bearings of 

 the shaft of the armature, h, is a disc of wood or ivory to brace 

 the upright stem e. c, is one termination of the magnet coil, 

 serving as a conducting spring, d, is the other conducting spring 

 passing through the disc 6, into the cup n, for battery connexion. 

 The other termination of the magnet wires passes into the cup^. 

 At c, c?, 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 c?, plays upon the dissected part, whose metallic divisions 

 are so arranged that they shall come into contact with the spring 

 €?, when the armature is a little inclined from right angles to the 

 plane of the magnet, and leave spring c?, 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 artnature 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 w, 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 small powers, such as turn- 

 ing lathes, &c. it probably will be effected by either the revolving 

 or vibrating armature machines. 



Reciprocating Armature Engine. 



Figure 6, represents an electro-magnetic engine with vibrating 

 or reciprocating armatures. «, «, are the electro-magnets, firmly 

 secured to the base board and the wooden table t. b, b, are the 

 armatures of soft iron connected with the shaft (cZ) 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 f?i. It is simple in construction, 



