[Illustration: FIG. 2. DOUBLE REDUCTION.] [Illustration: FIG. 3. SINGLE REDUCTION.] In the majority of American vehicles the motion of the motor is transmitted to the wheels by means of spur gearing. In some cases a single motor is used, in others two; and in one or two designs that have come to public notice, four motors are employed, one for each wheel of the carriage. Fig. 2 illustrates what is commonly called a double reduction gear for single motor equipment. The outline _A_ represents the motor, _B_ being the shaft. Upon this shaft is mounted a small pinion which meshes into a larger wheel on the intermediate shaft _C_. This shaft carries a pinion which meshes into the wheel _D_ mounted upon the axle of the vehicle. Fig. 3 illustrates a single reduction double motor equipment, the motors being located at _AA_. In this arrangement the pinion on the end of the motor shaft meshes directly into a large gear secured to the carriage wheel, thus dispensing with the intermediate shaft _C_ of the previous figure. The single reduction gear is the more simple in construction, but the motors run at a lower velocity, and on that account must be larger for the same capacity. With the double motor construction each wheel is driven independently and the axle _C_, in Fig. 3, remains stationary, as in any ordinary vehicle; but in a single motor equipment, arranged as in Fig. 2, the wheels are fastened to the axle and the latter rotates. When a carriage runs round a short curve the outer wheels will revolve faster than the inner ones, if free to move independently, as in Fig. 3. If they are rigidly attached to the axle, as in Fig. 2, one or the other will have to slide over the ground, and this is decidedly objectionable with rubber tires. To prevent this slipping of the wheels in rounding curves, the axles, in designs following the construction of Fig. 2, are made in two parts, and the gear _D_ is arranged so as to drive the two halves, imparting to each one the proper velocity. Gear wheels of this kind are called compensating gears; they are made in many designs, but the most common form is that illustrated in Fig. 4. In this drawing _A_ is the gear _D_ of Fig. 2, and _BB_ are bevel gears which are mounted upon studs _C_, which are virtually the spokes of wheel _AA_. Large bevel gears _E_ and _F_ are placed on either side of _A_ _E_, being secured to _G_, which is one-half of the axle, and _F_ and _H_, which is the other half. If the carriage is running in a straight line, the two parts of the axle _G_ and _H_ will revolve at the same velocity and the gears _BB_ will not revolve around the studs _C_, but in rounding a curve one of the halves of the axle will revolve faster than the other and then the gears _B_ will rotate round the studs _C_. The compensating gear is not a feature peculiar to electric vehicles; it is used on all kinds of automobiles when the construction is such as to require it. [Illustration: FIG. 4. COMPENSATING GEARS.]