changes at each passage in front of a pole piece.  The ends of the wire coinciding with the horizontal diameter of the ring are stripped of the gutta percha, and are connected to copper wires which are twisted together and around two copper rods, which are placed vertically, their lower ends entering two small cavities made in the base of the apparatus.  The circuit is thus continuous with two ends at opposite points of the same diameter.  The ring is about 1.1 in. thick, and is fixed, as shown, to two wooden columns, B B, by two blocks of copper, a.

[Illustration:  The Elias electromotor.—­Made in 1842.]

It will be seen from the mode of coiling the wire on this ring, that if a battery be connected by means of the copper rods, the current will create six consecutive poles on the various projecting blocks.  The inner ring, E, is about 11 in. in outside diameter, and is also provided with a series of six projecting pieces which pass before those on the exterior ring with very little clearance.  Between these projections the space between the inner face of the outer, and the outer face of the inner ring, is 0.40 in.  The latter is movable, and is supported by three wooden arms, F, fixed to a boss, G, which is traversed by a spindle supported in bearings by the columns, A and C. A coil is rolled around the ring in exactly the same way as that on the outer ring, the wire being of the same size, and the insulation of the same thickness.  The ends of the wire are also bared at points of the diameter opposite each other, and the coil connected in pairs so as to form a continuous circuit.  At the two points of junction they are connected with a hexagonal commutator placed on the central spindle, one end corresponding to the sides 1, 3, and 5, and the other to the sides 2, 4, and 6.  Two copper rods, J, fixed on the base to two plates of copper furnished with binding screws, are widened and flattened at their upper ends to rest against opposite parallel sides of the hexagon.  It will be seen that if the battery is put in circuit by means of the binding screws, the current in the interior ring will determine six consecutive poles, the names of which will change as the commutator plates come into contact successively with the sides of the hexagon.  Consequently, if at first the pole-pieces opposite each other are magnetized with the same polarity, a repulsion between them will be set up which will set the inner ring in motion, and the effect will be increased on account of the attraction of the next pole of the outer ring.  At the moment when the pole piece thus attracted comes into the field of the pole of opposite polarity, the action of the commutator will change its magnetization, while that of the pole-piece on the fixed ring always remains the same; the same phenomenon of repulsion will be produced, and the inner ring will continue its movement in the same direction, and so on.  To the attractive and repulsive action of the magnetic