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INVENTIONS OF NIKOLA TESLA.

bronze ring and the rim of the wheel, respectively. The wholemay then be taken off and forms a solid structure. The con-ductors in such a type of machine should consist of sheet copper,the thickness of which, of course, depends on the thickness ofthe pole projections; or else twisted thin wires should he em-ployed.

Fig. 99 is a smaller machine, in many respects similar to theformer, only here the armature conductors and the exciting coilare kept stationary, while only a block of wrought iron is re-volved.

It would be uselessly lengthening this description were I to

Fin. 98.

mm

dwell more on the details of construction of these machines.Besides, they have been described somewhat more elaborately inThe Electrical Engineer , of March 18, 1891. I deem it well,however, to call the attention of the investigator to two things,the importance of which, though self evident, he is neverthelessapt to underestimate; namely, to the local action in the con-ductors which must be carefully avoided, and to the clearance,which must be small. I may add, that since it is desirable to usevery high peripheral speeds, the armature should be of verylarge diameter in order to avoid impracticable belt speeds. Of