Torpedoes and Torpedo Warfare / Containing a Complete and Concise Account of the Rise and Progress of Submarine Warfare

by Charles William Sleeman

f.—Connect the line to terminal IV.

The galvanometer is then to be turned in the same direction as the needle is deflected until the needle coincides with the zero point. Whilst this is being done the large scale on the slate disc will move under the pointer Z, which must be left stationary; the sine of the angle indicated by Z will thus give the value proportionate to the strength of the current. Should the shunt box be required, it has to be connected with terminals II. and IV.

[Fig. 4] shows the same connections as [Fig. 7], but without the shunt box, and with the battery commutator. Fig. 3_a shows diagram of the same connections but with the key K, and [Fig. 3_b] the same without the key.

A Shunt.—A "Shunt" is a second path offered to a current traversing a given circuit, or portion of a circuit, so as to diminish the amount of the current flowing through that portion of the circuit. In the diagram shown at [Fig. 89] the shunt diminishes the amount of the current flowing along the circuit between A and B.

If only 1/Nth of the current is to pass along the circuit between A and B (of resistance R) then the resistance of the shunt must equal R/(N - 1).

By the aid of shunts it is quite possible to make use of very sensitive instruments to measure powerful currents.

Commutators or Switch Plates.—A commutator or switch plate is an apparatus by which the direction of currents may be changed at will, or by which they may be opened or closed. Bertin's commutator, which is represented at [Fig. 90], consists of a small base of hard wood on which is an ebonite plate, this by means of the handle m is turned about a central axis between two stops c and c'. On the disc are fixed two copper plates, one of which o is always positive, being connected by the axis and by a plate (+) with the binding screw P, which receives the positive electrode of the battery; the other copper plate i, e, bent in the form of a horse-shoe, is connected by friction below the disc with a plate (-), which plate is connected with the negative electrode N. On the opposite side of the board are two binding screws b, and b', to which are attached two elastic metal plates r, and r'.

On the disc being turned as shown in the figure, the current coming by the binding screw P passes into the piece o, the plate r, and finally the binding screw b, which by means of a copper wire leads the current to the apparatus in connection with b; then returning to the binding screw b', the current reaches the plate r', the piece i, e, and so to the battery by the binding screw N.

If the disc is turned so that the handle m is half way between c and c', the pieces o and i, e, being no longer in contact with the plates r and r', the current will not pass. If m is turned as far as c, the plate o will then touch r', and the current pass to b', and return by b, thus reversing its direction.