Messrs. Gent, of Leicester, have also patented a device in connection with this form of indicator, which we give in the patentee's own words:—"The objection so
frequently urged against the use of Electric Bells, that the servants cannot be depended upon to perform the operation of replacing the signals, cannot any longer apply, for the pendulum signals require no attention whatever. It consists of an electro-magnet having forks standing up in which V openings are made. An armature of soft iron, with a piece of thin steel projecting at each end lies suspended at the bottom of the V opening, a brass stem carrying the signal card is screwed into the armature, the action being, that when a current is allowed to pass through the electro-magnet the armature with the pendulum is drawn towards it and held there until the current ceases to pass, when it instantly looses its hold of the armature, which swings away and continues to oscillate for two or three minutes, so that if the servant happens to be out of the way, it may be seen on her return which pendulum has been set in motion. The Pendulum Indicator we have recently patented is entirely self-contained. The magnet has its projecting poles riveted into the brass base which carries the flag. The flag is constructed as [Fig. 70], but swings in closed bearings, which prevents its jerking out of its place, and enables us to send it out in position ready for use. It will be seen this patented improvement makes all screws and plates as formerly used for securing the parts unnecessary. It will be seen at once that this is simplicity itself, and has nothing about it which may by any possibility be put out of order, either by warping or shrinking of the case or carelessness of attendants."
Fig. 71.
There is only one point that needs further notice
with regard to these pendulum indicators, and that is, that since the rapid break and make contact of the ringing bell interferes somewhat with the proper action of the indicator magnet, it is always advisable to work the indicator by means of a relay (fixed in the same frame) and a local battery. This is shown in [Fig. 71], where a second pair of wires attached to C and C, to the extreme right of the indicator frame, are brought from the same battery to work the indicator and contained relay. It is not advisable, however, with the pendulum indicator, to use the same battery for the indicator; the relay should throw a local battery into the indicator circuit. In [Fig. 71] six pushes are shown to the left of the indicator frame. These, of course, are supposed to be in as many different rooms.
