234. Connections. If you join a Wheatstone's bridge, for example, with U and V (Fig. 106), the resistance added will be but 1 Ohm; if you join with U and W, the coils A and B will be in the circuit and make 3 Ohms resistance; if V and X, 4 Ohms; if V and Y, 9 Ohms; if U and Z, the whole, or 20 Ohms.
235. Resistance Coils. For use in some experiments in comparing the resistance, diameter, lengths, etc., of wires (See text-book), it is very handy to have coils made a certain number of meters long. (The meter is a French unit of measure and represents 39·3705 of our inches). German-silver wire has a much greater resistance than copper wire of the same size and length.
(a) Make a coil ([See App. 131] for method) containing 1 meter of No. 30 German-silver wire.
(b) Make a coil with 2 meters No. 30 German-silver wire.
(c) Make one with 2 meters of No. 28 German-silver wire.
(d) Make one with 20 meters of No. 30 copper wire.
The above wire must be insulated if it is to be wound upon spools. Bare wire may be arranged on boards or racks so that the current may not be short circuited.