bright, the points of contact should be tipped with platinum. Another form of contact to be let in the floor of the dining-room, within easy reach of the foot of the carver, or other persons at the head of the table, is shown at [Fig. 49 B].
Fig. 49 A.
Fig. 49 B.
Mr. Mackenzie has introduced a very ingenious contrivance whereby the ringer may know whether the bell at the distant end has rung. This is effected by inclosing in the push a device similar to that shown at [Fig. 43 A]. That is to say, an electro-magnet wound with wire, and surmounted by a thin iron disc, is placed in circuit with the line wires. The ringing of the bell rapidly magnetises and demagnetises the electro-magnet, and causes a humming sound, which clearly indicates whether the bell is ringing or not. As this device can be made very small, compact, and not liable to derangement, it is of easy application.