C1IAPTEJI XVI.

Motor With Equal Magnetic Energies in Field andArmature.

Let it be assumed that the energy as represented in the magnet-ism in the held of a given rotating held motor is ninety andthat of the armature ten. The sum of these quantities, whichrepresents the total energy expended in driving the motor, isone hundred; but, assuming that the motor be so constructedthat the energy in the held is represented by fifty, and that inthe armature by fifty, the sum is still one hundred; but while inthe first instance the product is nine hundred, in the second it is

Fig. 67.

two thousand five hundred, and as the energy developed is inproportion to these products it is clear that those motors are themost efficient—other things being equal—in which the magneticenergies developed in the armature and field are equal. Theseresults Mr. Tesla obtains by using the same amount of copper orampere turns in both elements when the cores of both are equal,or approximately so, and the same current energizes both; or incases where the currents in one element are induced to those ofthe other he uses in the induced coils an excess of copper overthat in the primary element or conductor.

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