§ 48. The continuous ringing bell is the modification which next demands our attention. In this, the ringing action, when once started by the push,[12] or other contact maker, having been touched, continues either until the battery is exhausted, or until it is stopped by the person in charge. The great use of this arrangement
is self-evident in cases of burglar alarms, watchman's alarms, etc., as the continuous ringing gives notice that the "call" has not received attention. The continuous ringing bell differs but little from the ordinary trembling bell. The chief difference lies in the addition of an automatic device whereby contact is kept up with the battery, even after the "push" contact has ceased. As it is desirable for the person in charge to be able to stop the ringing at will, without proceeding to the place where the "push" stands, so it is not usual to make the continuous ringing arrangement dependent on the "push," though, of course, this could be done, by causing it to engage in a catch, which would keep up the contact, when once made. Continuous ringing bells may be conveniently divided into two classes; viz., 1st, those in which a device is attached to the framework of the bell; which device, when once upset by the first stroke of the bell, places the bell in direct communication with the battery independent of the "push" or usual contact; and 2ndly, those in which a separate device is used, for the same purpose. This latter arrangement admits of the use of an ordinary trembling bell.
Fig. 35.
Fig. 36.
[Fig. 35] illustrates the action of bells of the first class. In the first place it will be noticed that there are three binding screws instead of two, as in the ordinary pattern, one marked C connected as usual with the carbon element of the battery; another marked L, which connects with line wire, and a third, Z, connected by means of a branch wire (shunt wire),