ELECTRICITY IN CAR.

Press, Volume LXIII, Issue 19149, 4 November 1927, Page 4

ELECTRICITY IN CAR.

POSSIBLE DANGERS. Definite evidence has been obtained from time to time that a car can become charged with static electricity, which may bo non-technically defined as "electricity at rest." To the scientist the condition is a specially interesting one, and it is certain that much has yet to bo found out concerning this remarkable phenomenon. At the outset it should, be made clear that the static electrification of a car lias nothing to do with the electrical equipment or its operation. A circumstance which accounts for much is the fact that a car is electrically insulated from the earth by its rubber tyres, • provided these arc in a dry state. A recent instance, which is vouched for. by • the "Motor," England, is that of a car becoming so highly electrically, charged by brake fiction as to cause a very smart shock accompanied by a snapping spark on touching the brake drum. Here is an interesting instance of the conservation of mechanical energy by friction between metal.and fabric into a powerful static charge, and it is probably a very, frequent condition in the ordinary everyday use of a car. Some few years ago a large car was destroyed by fire when filling up with petrol. The owner stated that ho -aw a mysterious spark jump across the tank opening to the fur.viel when tilling up, and this caused ignition of the petrol. Only, a static charge could account for it.

Another remarkable fact is that such phenomena may easily arise from atmospheric electricity. It is a wellknown fact that the atmosphere, even at no greater height than an ordinary wireless aerial, is at times so highly charged with static electricity a# # vo cause sparks and shocks on touching the terminals of a crystal set. The inference is that a large metal mass such as a car must necessarily often become charged by induction from an electrical atmosphere, and even, to so high a potential in a dry atmosphere as to give rise to sparks and severe shocks. So far as the petrol fire risk is concerned, if such conditions arise, the only real precaution is to "earth" the tank thoroughly by means_ of a wire connecting it to a water pipe or other well-earthed metal object, and thereby 'discharge the static electricity before any petrol is poured in.