378

INVENTIONS OF NIKOLA TESLA.

207, is preferable. The principal advantage of this type ofmachine is that there is not much magnetic leakage, and that afield may be produced, varying greatly in intensity in places notmuch distant from each other.

In these engravings, Figs. 204 and 205 illustrate a machine inwhich the armature conductor and field coils are stationary, whilethe field magnet core revolves. Fig. 200 shows a machineembodying the same plan of construction, but having a stationaryfield magnet and rotary armature.

The conductor in which the currents are induced may bearranged in various ways; but Mr. Tesla prefers the followingmethod : lie employs an annular plate of copper d, and by

Fig. 205.

means of a saw cuts in it radial slots from one edge nearlythrough to the other, beginning alternately from opposite edges.Hi this way a continuous zigzag conductor is formed. When thepolar projections are f inch wide, the width of the conductorshould not, under any circumstances, be more than inch wide;even then the eddy effect is considerable.

To the inner edge of this plate are secured two rings of non-magnetic metal e, which are insulated from the copper conductor,but held firmly thereto by means of the bolts f. Within therings e is then placed an annular coil g, which is the energizingcoil for the field magnet. The conductor n and the parts at-tached thereto are supported by means of the cylindrical shell or