and the leading wires of the lamp are connected with C and with Z as explained.
(b) When working singly and revolving in the direction indicated in Fig. 168:—
| M | is connected to | B', |
| M' | " | B, |
| m | " | Z, |
| m' | " | C. |
Thus the only change necessary when the machine is to be driven in the opposite direction to that for which it is made, is to disconnect at B the wire from M to B and at B' the wire from M' to B', and to cross them. The machine will then be connected as above (b).
(c) When working two machines in parallel circuit, as in [Fig. 174], they must be connected as follows (that on the left of the page being called the first machine, and that on the right the second machine):—
| C | of first to | C | of the second. |
| Z | " | Z | " |
| M | " | B | " |
| B | " | M | " |
| M' | " | B' | " |
| B' | " | M' | " |
and then connect C and Z of the second machine with the leading wires of the lamp.
The connections m to Z and m' to C in each machine are the same as in cases (a) and (b). They do not require to be altered, and may therefore be left out of consideration in all three cases (a), (b), and (c). The whole of the connections here indicated can be quickly made by means of a cross-bar commutator or switch, which is supplied with the machines in cases where such changes are likely to be required frequently. This is usually attached to a wall, leading wires being taken to it from the dynamo machines separately, and others from the switch being led to the electric lamps.
The leading wires from machine to lamp should, whenever possible, be kept separate, to prevent them rubbing together and making contact. A distance of two inches is quite sufficient to prevent accidents of any kind.