Fig. 75.
§ 71. The wires having been laid by any of the methods indicated in the preceding five sections, the fixer is now in a position to connect up. No two houses or offices will admit of this being done in exactly the same way; but in the following sections most of the possible cases are described and illustrated, and the intelligent fixer will find no difficulty, when he has once grasped the principle, in making those trifling modifications which the particular requirements may render necessary. The first and simplest form, which engages our attention, is that of a single bell, battery, and push, connected by wire only. This is illustrated at [Fig. 75]. Here we see that the bell is connected by means of one of the wires to the zinc pole of the battery, the push or other contact being connected to the carbon pole of the same battery. A second wire unites the other screw of the push or contact with the second binding screw of the bell. There is no complete circuit until the push is pressed, when the current circulates from the carbon or positive pole of the battery, through the
contact springs of the push, along the wire to the bell, and then back again through the under wire to the zinc or negative pole of the battery.[15] It must be clearly understood that the exact position of battery, bell, and push is quite immaterial. What is essential is, that the relative connections between battery, bell, and push be maintained unaltered. [Fig. 76] shows the next simplest case, viz., that in which a single bell and push are worked by a single cell through an "earth" return (see [§ 70]). Here the current is made to pass from the carbon pole of the battery to the push, thence along the line wire to the bell. After passing through the bell, it goes to the right-hand earth-plate E, passing through the soil till it reaches the left-hand earth-plate E, thence back to the zinc pole of the battery. It is of no consequence to the working of the bell whether the battery be placed between the push and the left-hand earth-plate, or between the bell and the right-hand earth-plate; indeed, some operators prefer to keep the battery as near to the bell as possible. At [Fig. 77] is shown the mode by which a single battery and single bell can be made to ring from two (or more) pushes situated in different rooms. Here it is evident that, whichever of the two
pushes be pressed, the current finds its way to the bell by the upper wire, and back home again through the lower wire; and, even if both pushes are down at once, the bell rings just the same, for both pushes lead from the same pole of the battery (the carbon) to the same wire (the line wire).
Fig. 76.