external current which works the motor, when the motor is kept at rest. If it is now allowed to move, its motion produces, in virtue of the laws of induction, a current in the circuit of intensity, i1, in the opposite direction to the external current; the effective intensity of the current traversing the circuit is thus reduced to i - i1. The intensity of the counter current is given, like that of the generating current, by the equation, i1²R = i1 [omega]1 M1 C1, or i1R = [omega]1 M1 C1, the index, 1, denoting the quantities relating to the motor. Here M1 C1 is a function of i - i1, not of i. As in a generator the force transformed into electricity has a value, i [omega] M C, so in a motor the force developed by electricity is (i - i1) [omega]1 M1 C1. On account, however, of the losses which occur, the effective power, that is the disposable power on the shaft of the motor, will have a smaller value, and in order to arrive at it a coefficient of efficiency, K1, must be added. We shall then have W1 = K1 (i-i1) [omega]1 M1 C1. The author has no knowledge of any experiments having been made for obtaining this efficiency, K1. Next let us suppose that the current feeding the motor is furnished by a generator, so that actual transmission by electricity is taking place. The circuit, whose resistance is R, comprises the coils, both fixed and movable, of the generator and motor, and of the conductors which connect them. The intensity of the current which traverses the circuit had the value, i, when the motor was at rest; by the working of the motor it is reduced to i - i1. The power applied to the generator is itself reduced to W-[(i-i1)[omega] M C]/K. The prime mover is relieved by the action of the counter current, precisely as the consumption of zinc in the battery would be reduced by the same cause, if the battery was the source of the current. The efficiency of the transmission is W1/W. Calculation shows that it is expressed by the following equations:W1/W = K K1 [([omega]11 M1 C1)/([omega]1 M C)], or = K K1 [([omega]11 M1 C)/([omega]11 M1 C1 + (i-i1) R)]; expressions in which it must be remembered M C and M1 C1 are really functions of (i-i1). This efficiency is, then, the product of three distinct factors, each evidently less than unity, namely, the efficiency belonging to the generator, the efficiency belonging to the motor, and a third factor depending on the rate of rotation of the motor and the resistance of the circuit. The influence which these elements exert on the value of the third factor cannot be estimated, unless the law is first known according to which the magnetisms, M C, M1 C C1, vary with the intensity of the current. GENERAL RESULTS.