Richardson's handbook of projection (1927)

MANAGKRS AND PROJFXTIONIS IS 437 ters one binding post, the right-hand one we will assume, passes through the dial switch lever and from it into contact No. 1, which connects with one end of the coil banks. It passes through all the coils of the right hand bank, through the jumper and through all the coils of the left hand bank, whence it passes to the arc, the end of the last coil (14) connecting to left hand binding post. This places the two sides of the rheostat in series and makes it available for use on current up to 240 volts pressure. In diagram B, Fig. 142, we see the two banks connected to the arc in multiple, the circuit wire being connected to the jumper, as shown, so that each of the two banks of coils become in effect a separate rheostat, as per Figs. 137 and 138. This method is, of course, not available for more than 110-volt pressure. By its use we get the full capacity of the two banks of coils. When using either one of the connections shown at A or B, Fig. 142, the lever must be placed on contact 1, though unless the coils show red with the lever on contact 1 it may be moved to contact 2, 3, etc., until the coils begin to show red in a dark room, to increase current flow. Of course, in practice, the wire would not be actually connected to the jumper, as in B, but branched, with one branch connected to each binding post, the jumper being removed. In considering the selection of a rheostat for road use we would suggest that you investigate the merits of "New Rheostat," a description of which follows. All projector manufacturers carry rheostats of standard size in stock, and can provide rheostats of special design or capacity on short notice. MULTIPLE COIL RHEOSTAT.— In 1921 a resistance unit, ideal for projection work came on the market, the general Figure 144.