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306 it requires some special experience to know whether a battery really requires renewal, whether the positive plates only should be renewed, or in fact how it should be treated.

Failure of connection between the controller, cylinder, and the contact springs may also give rise to stoppage. That is very easily tested by putting the controller in the position in which the car refuses to move, and testing the contact springs by pressing them against the cylinder. If the car then goes on they require tightening.

If the batteries and motors are all right in any particular position, and the car refuses to move even when the controller is tested in the above-described manner, there may be failure in the connections. Whether this is so or not can to a certain extent be judged by noticing whether the controller sparks when moved from one position to another. If it does so the current is passing and the connections are presumably all right; otherwise the connections are probably faulty. They can be conveniently tested with a dry cell and galvanometer in the same way as the motor is described above as being examined. Heating at any point is usually the effect of a loose contact.

If the conducting cables are badly arranged, so as to rub on any metallic portion of the car, the insulation may be worn through and short circuiting ultimately result. It is therefore of the greatest importance to see that no such contact of the cables with any portion of the car ever occurs.

Similarly, accumulator connections should preferably only be made to the nesting-boxes and the connections with the cables made from contacts on these.

Electric vehicles can be charged in two ways, either by connecting the car directly to a suitable source of current, or by employing two or more batteries, one of which is always kept charged at the charging station, the arrangement being that when the battery on the car is run down it is taken out and a freshly charged battery inserted. This latter arrangement is usually only practised in stations or 'garages' where a number of cars are kept. Charging on the car is a much more