122 An account of the Electro- Magnetic Engine. 



means of filing or hammering may possibly prove injurious, by hard- 

 ening the surface of the iron, and thereby rendering it less susceptible 

 of magnetism. The form given in the plate is attended with some 

 other inconveniences, as regards the formation of the spiral line of 

 copper wire, which must be first bent over another cylinder of the same 

 dimensions. These spirals must be quite close to the cylinder, but 

 be preserved from contact with it by being wrapped in silk for the 

 sake of isolation. In future the arrangements represented in figure 2, 

 will be preferred, in which // are stationary cylinders, and m m the 

 cylinders revolving round the axle d. By this means cylindrical bars 

 of soft iron may be used, to obtain which can be a matter of no diffi- 

 culty, as they are to be had of all dimensions ready formed. There will 

 then be nothing further necessary than to cut them to the proper 

 length, and bend the spirals round them by means of a lathe or 

 otherwise. 



The several bars attached to the moveable and stationary frames are 

 then converted into electro-magnets, by being encircled by the wire of a 

 voltaic battery, and their extremities are north and south poles alter- 

 nately. If, then, a slight impulse be given to the moveable frame, 

 it will continue to revolve in the direction given, until the contrary 

 poles come opposite one another, after a few oscillations the motion 

 would be suspended, were it not, that, by means of an ingenious con- 

 trivance of Jacobi, which he terms the " Commutator " the moment dis- 

 similar poles come opposite one another, the poles of the moveable or 

 stationary bars are reversed, and thus the original conditions of motion 

 are renewed. 



Figure 3 gives a side and a front view of the Commutator, abed are 

 four plates of copper, attached to the rotatory axle, e e, which likewise 

 bears the frame on which the electro-magnets are fastened ; the plates 

 a and b, as well as the plates c and d, are connected by copper tubes, 

 / /, and each pair of plates perfectly separated from the other by the 

 interposition of a hollow axle of japanned wood, or any similar isolat- 

 ing substance. The edge of each plate is accurately divided into eight 

 parts, four of which, h h h h, are cut out, and duly filled with ebony, so 

 that the sectors and the metal present a perfectly even surface. The 

 plates are so arranged on the axle, that the sectors of wood and metal 

 alternately correspond? as exhibited by the figure, Z Z. C C, are 

 copper levers, very moveable round their axes, and serving to conduct 

 the current of the voltaic battery. Each lever is shaped like a hammer 

 at the end, which rests on a corresponding plate. The shorter arm is 

 bent, and dips into the vessel k, filled with mercury. The vessels k k 



