=Table Pushes.=--Call bells to be rung from the dining-room table are connected with an annunciator or to a separate bell. The table pushes may be temporarily clamped on the edge of the table and connected by a cord to an attachment set in the floor or the connection may be made by a foot plate set on the floor. In Fig. 247 is shown a form of push _P_ which is intended to be clamped to the edge of the table under the cloth. The plate _F_ forms the floor connection. It is set permanently with the upper edge flush with the surface of the floor. The part _S_, in which the connecting cord terminates, when inserted in the floor plate, makes contact at the points _C_ to form an electric circuit with the battery. The foot plate shown in Fig. 248 is only an enlarged push button which is set under the table in convenient positions to be pressed with the foot. Its connection might be made as indicated or with the same floor connection as that of the preceding figure. Fig. 249 is a simpler form of floor push in which a metallic plug is inserted in the floor plate. When the plug _R_ is pressed, contact is made at the points _C_ to form the circuit with the battery and bell. [Illustration: FIG. 246.--A kitchen annunciator. FIG. 247.--Plug attachment and table push for a dining table. FIG. 248.--Foot plate and contact for table bell. FIG. 249.--Call bell attachment with detachable contact piece.] =Bell-ringing Transformers.=--The general employment of alternating electricity for all commercial service requiring distant transmission is because of the possibility of changing the voltage to suit any condition. The energy transmitted is determined by the amperes of current carried by the wires and the volts of pressure by which it is impelled. The product of these two factors determines the watts of energy transmitted. 110 volts × 1 ampere = 110 watts. If the voltage is raised to say ten times the original intensity with the same current, the quantity of energy is ten times the original amount. 1100 volts × 1 ampere = 1100 watts. The carrying capacity of wires is determined by the amperes of current that can be transmitted without heating. The cost of copper wire is such that the expense of large wires for carrying a large current is unnecessary where by raising the voltage a small wire will perform the same service; therefore, it is desirable to transmit electric energy at a high voltage and then transform it to suit the condition of usage. Alternating current may be transformed to a higher or a lower voltage to suit any condition by using step-up or step-down transformers.