ANNUAL ADDRESS. XXIII. 
armature revolves within one tenth of an inch of the poles of the 
magnet. 
Controller—To apply the current from the line wire to the 
motor, so that the car may be stopped, started, reversed, and for 
regulating the speed, it is first passed through a special form of 
compound switch called a controller, which consists of a cylinder 
with metallic strips or contact pieces fixed as arcs upon its 
surface. The necessary connections are thus made as the cylinder 
is revolved by means of a handle which corresponds to both 
regulator and notching up lever in the locomotive engine. 
If the full pressure of 500 volts were suddenly applied to the 
motors in a car, the cars would start so suddenly that the passengers 
would be injured, so that it is necessary to temper the pressure at 
starting, and apply to each motor less than half the total voltage, 
gradually increasing the pressure and thereby the speed of the car, 
until the maximum is reached. 
The General Electrical Company recommend their Series 
Parallel Controller in preference to the rheostatic method of 
control, ee 6 order to start the car the motors are first connected 
in “ series,” 7.¢., the circuit passes first through one motor and then 
the other Sais division. By this means (together with a very 
slight resistance which is instantly cut out) the proper starting 
pressure is applied without loss, and the motor being in series, the 
Same current that starts one flows through the other. After the 
car is started the voltage applied to each motor is increased by 
gradually throwing the motors into “ parallel,” i.<., the circuit is 
divided, one branch passing through each motor. At full speed” 
the motors are in parallel with no resistance in the circuit. 
The changes from series to parallel necessitate the breaking of 
heavy currents at a high potential in a limited space, and the 
Sparks or arcs produced would destroy the contact plates, fingers, 
cylinder, and all parts in the vicinity of the break; but the 
cylinder is embraced by a powerful magnet, which blows out the 
sparks immediately they tend to form. 
