manager or head of the establishment, who can thus, from time to time, satisfy himself of the watchman's vigilance. The record should be examined in the morning, and replaced by a clean sheet of card.
"This clock received the special mention of Her Majesty's Commissioners in Lunacy, and has been adopted by some of the largest asylums in the country.
"We have recently made an important improvement by adding a relay for every marker, thus enabling a local battery of greater power to be used for actuating the markers. This has made no alteration in the appearance of the clock, as the relays are contained within the cornice at the top of the clock case."
§ 60. By means of a float, it is possible to give notice of the height of water in a tank, a reservoir, or even of the state of the tide. In these cases all that is needed is a float with an arm, having a suitable contact attached, so that when the water rises to the level of the float and lifts it, it causes the contact piece to complete the circuit through a set screw. Or the float may be attached to an arm having a certain play in both directions, i.e., up and down, within which no contact is made, as the arm has a contact piece on either side, which can touch either an upper or a lower contact screw, according to whether the tide is low or high, or whether the lock or tank is nearly empty or too full.
Fig. 64.
§ 61. Sometimes it is convenient to be able to ring an ordinary trembling bell continuously, as when a master wishes to wake a member of his family or a servant; or again, to cut a given bell or bells out of
circuit altogether. The arrangements by which this can be effected, are known as "switches." Of switches there are two kinds, namely, plugswitches or interruptors, and lever switches. The former consists essentially in two stout plates of brass affixed to a base board of any insulating material. These brass plates are set parallel to each other, a short distance apart, and the centre of the facing edge is hollowed out to take a brass taper plug. A binding or other screw is fixed to each brass plate, to connect up to the leading wires. When the plug is in its socket, the circuit between the two plates (and consequently between the battery and bell, etc.) is complete; when the plug is out, the contact is broken. This form of switch is subject to work out of order, owing to the fact that the taper plug gradually widens the hole, so that the contact becomes uncertain or defective altogether. By far the better form of switch is the lever switch, as shown at [Fig. 64]. This consists in a movable metal lever or arm, which is held by a strong spring in contact with the upper binding screw. It can be made to slide over to the right or left of the centre, at its lower or free end, as far as the binding screws or studs shown, which act at once as stops and point of connection to wires. When the arm or lever is in the centre no contact is made but if it be pushed over to the right, it slides on a
brass strip let into and lying flush with the base. Contact is thus made between the upper binding screw and the left-hand screw. If there is another brass strip on the left-hand side (as shown in the figure), contact may be made with another bell, etc., by sliding the arm to the left; or again, if no metal strip be placed on the left side the contact may be broken by pushing the arm towards the left-hand stud.