to be avoided is a live rear axle with the motor so mounted that any large proportion of its weight comes on this live axle. This tends to cause distortion, with ultimate increased friction in the bearings and loss of efficiency. A very good system of mounting a single motor is illustrated by the recent De Dion vehicles, in which a single motor drives on to a separately supported compensating gear through an arbor-shaft, the compensating gear being connected to the driving wheels by jointed rods. This enables motor and compensating gear to be mounted on the upper side of the springs, both being thereby comparatively protected from vibration.
The advantages of a single motor are that it can be built with a somewhat higher efficiency than can be obtained with two separate motors, each of half the power. It is questionable whether there are any other advantages.
Cars employing two motors may have them mounted either to drive the front wheels, in which case the motors are necessarily mounted so as to turn with the wheels, or the motors may be mounted one to drive each of the rear wheels either by spur gearing (fig. 12) or by chains.
The Krièger cars are conspicuous examples of the former class, and are in fact the only electromobiles in this country in which this method of driving has been utilised. The disadvantages are that there is a tendency for the wheels to slip when the car is going uphill on greasy roads.
The latter class with two motors comprises an immense number of most conspicuous and successful vehicles, amongst which are those of the City and Suburban Electric Vehicle Co., Ltd. The advantages of two motors are numerous. In the first place, they practically ensure the car being supplied with sufficient motive power, as the limit in si/e of an efficient motor makes it practically certain that a car provided with two will be able to get along. In the second place, if anything happens to one of the motors at a distance from home, it is almost always possible at a sacrifice of speed to get home with one. Thirdly, a greater variety of speeds can be obtained; and
