448 KNIGHT DUNLAP 



current to give sure operation, and not enough to heat the motoi 

 seriously, or make starting difficult, is the easy requirement. 

 The motor will run on a single 60 watt lamp, although hard to 

 start on so small current, and easily put out of phase and stopped 

 by the slight jar of the clutch action. The current practically 

 needed depends on the adjustment of the clutch, and the amount 

 of current in the clutch circuit. On the average, lamps totaling 

 150 watts will do very well; 100 watts may be satisfactory; more 

 than 240 should never be used; and more than 180 will heat the 

 motor if used continuously. 



Lamp resistance is advised, because of its safety. The lamps 

 act as tell-tales, showing clearly whether the current is on or 

 off, and there is no danger of damage from accidentally putting 

 on too much current, as is apt to happen in moving a rheostat 

 handle in the wrong direction. By having the connections at 

 the lamp board covered, all danger from shock is eliminated. 



If a rheostat be used instead of lamp resistance, one of 120 

 ohms total resistance, and 2 amperes continuous capacity is 

 advised. The Jagabi 1506, James G. Biddle, fills these specifi- 

 cations. The resistance should never be allowed to fall below 

 50 ohms; hence a stop should be put on the slide, a little less 

 than half way from the zero end. 



The motor has been run experimentally on the whole range 

 of frequencies between 15 and 120 per second: the conditions for 

 this test were arranged by M. W. Pullen of the Department of 

 Electrical Engineering, and I have not standardized the resis- 

 tances to be used with the 25 cycle circuit. The determination 

 of the proper resistance is very simple, but there are probably 

 few places where this frequency would be available. 



The speed of the motor, when operated on the unrectified 60 

 cycle current may be too great. Since there are ten poles to 

 the motor, and the 60 cycle current has 120 impulses per second, 

 the armature will make 12 revolutions per second and the measur- 

 ing unit of the dial will be one twelve-hundredth of a second. 

 Not only is this unit needlessly small, even for the measurement 

 of simple reaction times, but the difficulty in starting the motor 

 is high (see below). With 25 cycle unrectified current the arma- 



