. Motion picture electricity. storage battery is only about 50 or 60 per cent, of theamount put in, but still it is a saving of at least 50 percent, of the amount generally wasted in the rheostat. Itcannot be said that this method of control is practical,although it may have its application in certain places andunder conditions suitable to it, and it may be of advan-tage to some readers to know that it is possible to use system may, however, be placed in the list withother impractical controlling devices for the direct currentprojector arc. MOTION PICTURE ELECTRICITY 161 Water Type.—-W
. Motion picture electricity. storage battery is only about 50 or 60 per cent, of theamount put in, but still it is a saving of at least 50 percent, of the amount generally wasted in the rheostat. Itcannot be said that this method of control is practical,although it may have its application in certain places andunder conditions suitable to it, and it may be of advan-tage to some readers to know that it is possible to use system may, however, be placed in the list withother impractical controlling devices for the direct currentprojector arc. MOTION PICTURE ELECTRICITY 161 Water Type.—-Where a resistance unit of the ordi-nary rheostat type is not available, it is possible to manu-facture for quick use a resistance unit which is composedof a barrel with a metal plate at the bottom to which isattached by means of a rubber covered cable one terminalof the circuit, and a second metal plate movable up anddown, to which is attached another wire to be connected TO LINE. in series with the arc lamp and the other terminal of theline. When such a device is filled with salt water, it willallow current to pass through the circuit. The strengthof current will depend upon the distance between the twometal plates and upon the amount of salt put in the an outfit is usually called a water rheostat and isillustrated in Fig. 96. The lower you set the upper plate, 162 MOTION PICTURE ELECTRICITY that is, the closer it is to the lower plate, the greater theamount of current that will flow; and the more salt thereis in the water, the lower will be the resistance of thewater, and consequently more current will flow. Waterrheostats are very useful, especially for the higher volt-ages, in case of an emergency, and operate fairly satis-factorily, although the water becomes heated in a shorttime and such rheostats require more or less attention. There are also other methods belonging to the imprac-tical list which I do not deem it necessary to refer to,
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