what the load may be, provided the voltage or pressure of the current supplied to it be the same; and it will consequently try its best to force a car provided with it through mud or uphill at the same pace as it would drive on the flat. The series motor, on the other hand, more or less apportions its speed to the load, and will go slower uphill and faster on the flat. The series motor has this additional advantage compared with the shunt motor, that it produces a greater starting torque or turn-
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Fig. 6
ing moment—that is to say, series motors are better calculated than shunt motors for starting a car from a state of rest or getting it out of difficulties. Generally speaking, we may say that, for automobile purposes, series motors and separately excited motors, which present some of the characteristics of a series motor, are to be preferred for the propulsion of vehicles.
The majority of motors actually employed in electromobiles have four poles, and the brushes which lead the current to the commutator are usually of carbon, held in special brush-holders
