Fig. 102.
221. Combination Buzzer and Telegraph Sounder. Fig. 102. This apparatus is good for experimental purposes, where you do not wish to go to the trouble to make two separate pieces. For the dimensions and explanations see [App. 121] and [125]. There is but a slight change in [App. 125] to make this.
222. Connections. The inside ends ([§ 123]) of the magnet wires are fastened together at S. The outside ends are joined to the two binding-posts, Y and Z, made like [App. 46]. A wire, P, joins Y with the screw in T, which is a piece of stiff tin or copper, which presses down upon the top of I. In this way a connection may always be had between I and T. A wire, R, joins F electrically with X; it is held under the head of the screw, G. ([See App. 125] about adjustments.)
223. Operation. When you wish to use the apparatus as a buzzer, join your battery wires to X and Z. If the current enters Z, it will pass through the magnet coils out to Y, through P, T, I, F, and R to X. If you use it as a telegraph sounder, join the battery wires to Y and Z. The current will then pass simply through the coils; it will not bother to go into P, F, etc., as it has no place it can escape. If used simply for experimental purposes almost any cell of sufficient strength will do. If for telegraph, use [App. 9]; if for buzzer, use an open circuit cell, as, for example, a dry cell.
CHAPTER XVI.
COMMUTATORS AND CURRENT REVERSERS.
224. Commutators and Current Reversers are useful in some experiments, as, for example, those with tangent galvanometers ([App. 116], [117]), in which readings are made with the current passing around the coil in one direction, and again made at once with the current reversed. The use of commutators on motors and dynamos should be understood. The reversers herein shown are, of course, not at all like those used on motors. Current reversers are used in connection with the needle-telegraph and many other instruments.