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MANAGERS AND PROJECTIONISTS 461
The right way to measure the temperature of a part is to bed the thermometer bulb in a ball of rather stiff putty, and then place the putty against the suspected part, leaving it a sufficient time for the putty to get as hot as the part is. This will cause the thermometer to accurately register the temperature of the part.
Roughly, as applies to projection rooms, we may say that any part that is not more than 50 degrees C. (90 degrees Fahr.) higher than the actual temperature of the room, is not exceeding the above named limt, and unless this limit be exceeded, the equipment will not be damaged.
NOTE.— To reduce Centigrade to Fahrenheit (C. to Fahr.) multiply the degrees Centigrade by 1.8 and then add 32. For instance, assuming a temperature of 40 degrees C., how much is it Fahr.? 40x1.8=72 and 72+32=104 degrees.
THE HERTNER TRANSVERTER.— The transverter needs no introduction. It is giving service in projection rooms all over this and other lands. It is of the "upright" type, in that its armature stands vertical, with the D. C. element at its upper end.
The generator is of the shunt wound commutating pole constant current type, the double arc machine being designed to maintain practically constant amperage under a variation of from 50 to 130 in voltage. In practice this means that the generator voltage rises from its normal of between 50 and 60 volts when one arc is operating, to from 100 to 130 volts when two arcs are burning, without causing any change in amperage. This is accomplished without the use of any resistance in series with the arc, the maintenance of constant amperage under variation in voltage being entirely automatic.
The motor is mounted in the same frame with, and immediately beneath, the generator. The motor and generator armatures are mounted on separate shafts, which same are coupled together in the following way : One half a flange coupling is fitted to the upper end of the motor armature shaft, and the other half to the lower end of the generator armature shaft. The hub of the fan which supplies ventilation is placed between the two halves of the coupling, and the whole is clamped together by bolts, so that the assembled unit, as a whole, comprises the generator armature (at the top), the fan between and the motor armature below, the power from the motor being transmitted to the generator armature by means of the coupling, which latter is so made that it can be