In all three systems the motor itself is suspended from the axle, which it turns; and the armature of the motor is parallel to the axle and nearest to the centre of the car. On the end of the armature is a small cogwheel which gears into the teeth of a larger wheel keyed to the axle, and this turns round the wheels of the car. A coiled spring supports the field-magnet of the motor, and when the driver turns the lever on to the top of the controller (which is a high box in front of each platform containing a series of wires connected with the motor), and switches on the current, the motor is lifted up on the first revolution of the armature, the coiled spring takes up the motion of the motor, and prevents the car starting with a jerk. The current, when done with, returns to the source of supply by the ordinary tram rails, which are specially connected at the joints for this purpose. It is maintained that for cheapness of construction, simplicity of operation, reliability in action, and flexibility in adaptation, this method is superior to all others. There was at one time a certain objection to it on æsthetic grounds. The earlier examples, when clumsy wooden posts and festoons of wire obstructed the view and seemed to choke up the street, undoubtedly justified the protest against the “overhead”; but now that slender iron poles, ornamental rather than otherwise, and, in some cases, rosettes attached to the houses, are used for the suspension of the trolley wire, people have become reconciled to the appearance of the thoroughfares, and no longer object to the apparatus. One more system, an ideal one, remains to be considered. It is that of the “Self-contained Car,” which carries a battery of secondary cells, whence the current for working the motors is taken as required. But, for the present, there are serious obstacles against its general application. The great weight of the accumulators leads to a disproportionate consumption of power, and involves heavy expenditure on the permanent way and in rolling-stock. The batteries must be recharged at frequent intervals, and must either be removed from the car--a troublesome process--or the car must be kept idle while the cells are revivified. Accumulators as a rule do not live long, and have to be renewed. Thus the working expenses are so heavy that, ideal as the system is, and delightful the smooth running of the cars, it does not pay commercially to adopt it, and we must wait patiently in the hope that one day a perfect and practical secondary battery will appear on the scenes. Great improvements in lightness and durability are in the air.