Fig. 77.
In [Fig. 78], we have a slight modification of the same arrangement, a front-door pull contact being inserted in the circuit; and here, in view of the probably increased resistance of longer distance, two cells are supposed to be employed instead of one, and these are coupled up in series ([§ 40]), in order to overcome this increased resistance.
Fig. 78.
The next case which may occur is where it is desired to ring two or more bells from one push. There are two manners of doing this. The first mode is to make the current divide itself between the two bells, which are then said to be "in parallel." This mode is well illustrated both at Figs. [79] and [80]. As in these cases the current has to divide itself among the bells, larger cells must be used, to provide for the larger demand; or
several cells may be coupled up in parallel ([§ 40]). At [Fig. 79] is shown the arrangement for two adjoining rooms; at [Fig. 80], that to be adopted when the rooms are at some distance apart. If, as shown at [Fig. 81], a switch similar to that figured in the cut [Fig. 64] be inserted at the point where the line wires converge to meet the push, it is possible for the person using the push to ring both bells at once, or to ring either the right-hand or the left-hand bell at will, according to whether he turns the arm of the switch-lever on to the right-hand or left-hand contact plate.
