April 5, 1889.] 



SCIENCE. 



253 



It has already been applied to a number of cases of practical 

 work, where it takes the place, for alternating-current work, of 

 variable resistances, while it saves the energy of the circuit. It is 

 also made self-adjusting, and can maintain a constant average of 

 alternating current over a variable resistance, such as a series of 

 incandescent or arc lamps connected across the terminals of a sys- 

 tem or machine of alternating character. 



It is based on the principle of the demagnetizing effect of a 

 closed coil or circuit parallel to the coil or circuit in which the in- 

 ductive resistance is to be varied ; the relation of position of the 

 two coils on a magnetizable core forming a closed magnetic cir- 

 cuit, or nearly so, being made variable. 



In Fig. I, //is an iron core, preferably of ring or endless form, 

 made of wire or laminse, suitably piled and insulated to avoid 

 Foucault currents ; C is a coil of insulated wire wound on the core, 

 as shown ; 5 is a closed band or coil around the ring, and ar- 

 ranged to be moved over the coil Cby a handle, H, and pivoted at 

 P when preferred, though it could simply be slipped along in some 

 cases. Let, now, an alternating current of fairly constant poten- 

 tial be feeding the lamps L, L, from a to b, with the coil C in cir- 

 cuit. If the closed coil or band, S, be brought down over the coil 

 C, very little re-action or self-induction will exist in the coil C; and, 

 if its resistance be low, the lights L, L, will be given their full bril- 

 liancy. If the coils S and C be now separated more and more by 

 moving one away from the other around the ring, the self-induction 

 of coil C progressively rises, and becomes greatest when coil 5 is 

 farthest removed from it. The lights are now dimmed as far as 

 possible, any gradation being obtained by setting the coil S in a 

 position with respect to coil C corresponding to the desired effect. 

 The action is smooth and very effective. If a switch, IV, be placed 

 in circuit with the coil 5 so as to be opened when it strikes a pin, 

 ^, suitably placed, and after the coils C and S have been widely 

 separated, the effect of coil C is further enhanced in dimming the 

 lights or in exerting a self-induction which checks the current in 

 any device with which the apparatus may be put in circuit. 



In Fig. 2 the devices are shown placed in series, with a primary 

 coil, P, of a transformer, whose secondary, B, feeds the lights L, 

 or other devices, with current. A very smooth and powerful re- 

 sisting effect may thus be obtained with moderate sizes of appara- 

 tus. 



If the directions of windings are made opposite, the two coils C 

 and S, as in Fig. 3, may be connected in series or multiple arc, and 

 the current led from a lo b through them. They should in such 

 cases be wound to have equal ampere turns capacity in magnetizing 

 the core /. When the coils are superposed, they will neutralize 

 one another's self-induction ; but, as they are separated, the self- 

 inductive kick or re-action will gradually increase. The variation 

 of induction or re-action is obtained without contacts and switches,, 

 and in a smooth and gradual manner. 



In the preceding figures the devices shown have been arranged 

 to be operated manually. The same devices, however, if the parts 

 are relatively free to move, give out, from alternating currents, a 

 mechanical power or pressure which may repel the coils apart. 

 To obtain a movement of coil S, or pressure tending to move it, 

 coil C has only to be put into an alternating-current circuits 

 Further, this repulsive power may be utilized to make the self-in- 

 duction self-adjusting, whereby there may be obtained a constant 

 current on the circuit of a set of lamps, or the like, even though 

 variations of voltage of current fed to them may occur. Thus, as 

 in Fig. 4, the source, a b, of current may be one which varies ia 

 potential, the coil C being put in series with a group of lamps, 

 L, L. In this case the copper band or closed circuit 5 is pivoted 

 freely at P, and counterpoised to a certain extent by a lever and 

 weight, ic, or other device, whose effect may be varied if need be. 

 Sometimes a spring, Z, may be used in addition (or even alone, if 

 of proper retractile effect), and suitable stops may be provided to 

 limit the range of movement. Suppose that the coil 5 is set, and 

 so balanced that, with a given current in coil C, it is repelled so as 

 to about half cover the coil C (or less, if the counter- forces K, Z, . 

 are properly adjusted), and that an increase of current, due to in- 

 creased potential, takes place in the circuit A. Coil C will more 

 strongly repel circuit or band S, and it will move partly up and 

 away, with the result of increased self-induction in coil C ; which 

 self-induction, if the parts are suitably adjusted, will approximately 

 restore the current strength to what it was before the change. A 

 fall of potential corrects itself by working in the reverse direction. 



The apparatus in this self-regulating or automatic form is to be 

 used in such circuits as are represented in Fig. 5, where wires a, b, 

 of constant or even somewhat variable potential difference, feed in. 

 multiple several separate series of lights, L, L', L", such as incan- 



^r 



descent or arc lights with alternating currents. Each series, cir- 

 cuit, or branch requires a constant current; and to insure this, 

 even though a light be cut out in any series, the automatic self- 

 inductors of Fig. 4 are placed in each branch or series at C, C, C'\ 

 where each acts, as described in connection with Fig. 4, to preserve 

 the current strength. Of course, the group L (Fig. 4), or series 

 L, L', L", may be replaced by a single light or translating device, 

 such as an arc-lamp, without affecting the result. This has been 

 indicated at A (Fig. 5), always assuming the potentials to be not 

 so excessive or so feeble as to exhaust the capacity for regulation 

 to be found in the device. 



In Figs. 6 and 7 the part /' " is of iron, as shown, and carries 



