THE MONOBLAST WARNING DEVICE.
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THE use of electric horns or sirens has often been advocated, in connection with public-service .,. vehicles for the convenience of passengers, and-Aen the K-type bus was first brought out it was fitted with an electric horn. The stumbling block in the way of its development is that the police forbid the use of a warning device which can be sounded continuously, as is the case with an electric horn, with the result that up to the, present it has been found impossible to use such devices.
The High Tension Co., 62, Belvedere Road, S.E.1, knowing these police restrictions, set to work to perfect an instrument which would allow of the electric horn being sounded in short blasts only. The fitment they devised is remarkably neat and. simple, and is incorporated with the usual plunger which completes the electrical circuit.
The device consists of a plated brass tube containing two pistons provided with leather washers. The upper piston is connected directly by a rod to the operating knob, whilst the lower is supported by a spring, and a spindle which bears in an insulated bush provided with a stop pin preventing the piston from rising too far. This insulating bush carries the terminals for connecting to the operating batteries, and electrical connection is established between these terminals by the metal end of the lower piston spindle. Normally this end is held out of contact by the action of the spring. When the upper piston is forced down by means of the knob, air is compressed between the two pistons, and the lower, being forced downwards Ce against the connection of this spring, the electric circuit is completed, consequently sounding the born. The air, however, escapes past the upper piston, and the lower then rises owing to the pressure of its spring, thus breaking contact. It has been found unnecessary to make any special provision in the upper piston to allow this escape-of air, as it passes the leather.washer at such a speed that the blast of the horn is not unduly prolonged. To give another wgrning the knob must be pressed again.
The device has been protected by My. Codd, of the High Tension Co., and a certain number of these instruments is being fitted to the K-type omnibuses with a view to their adoption as standard. They will be used only in conjunction with the Smith " Eeho " horn, which iv made by the company.