Page:Popular Science Monthly Volume 91.djvu/185

 Popular Science Monthly 169

Storage batteries are A Tell -Tale Light System— First Assist- ant to the Motorcycle Cop

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turned on to drive the electric propelling motors. Electric machinery must be used under water because the oil engines con- sume precious air and exhaust poisonous gases.

On the next word from the captain, water from outside is al- lowed to fill the huge bal- last tanks in the central hull. Other ballast tanks at the ends of the boat are partially filled to hold the ship on an even keel. This trim- ming of the submarine, course, can be deli- cately controlled by the buoyancy gages and controls in the operating room. The weight of all this water causes the submarine to sink, but not com- pletely. The hori- zontal rudders at the stern of the ship are used to give the final touches to the dive. The com- mander directs the man at the wheel how far down he wishes to go. By watching the depth gages in front of him, the wheelman can so tip the diving rudders that the proper depth can be found immediately and held exactly.

It takes but a minute or two to dive. In torpedoing a ship, the entire vessel must be turned to aim the torpedo tubes, which lie parallel with the central axis of the sub- marine, in the bow. The command is given to fire. The gunners in the forward com- partment receive the order through speak- ing tubes or telephones. The torpedo is dis- charged from its tube by compressed air.

��Storage battery current is suf- ficient to run the system and also to operate a tonneau ex- tension of the colored lights

��PERMANENT ,

RED LIGHT

30 MILES- _

WHITE LIGHT-' GREEN LIGHT ^BLUE LIGHT

21T0Z5 MILE5 lb TO 20 MILES 15 MILES

���Details of the mechanism by which the passengers and traffic policemen can be kept informed as to the speed of the car

��IT would profit the French General Staff as much to have one of its members an agent of the German Intelligence Bureau as it would profit a motorist, bent on speed- ing, to display this tell-tale electric signal on the front of his ma- chine.

The device consists of a series of col- ored lights, five in num- ber, arranged perpendic- ularly in a metal case, and mecha- nism essen- tially similar to that of a speedo- meter.

When the auto- mobile to which this signal is affixed moves at a rate of less than ten miles an hour, no light shows. From ten to fifteen miles an hour is indicated by an amber lamp. At fifteen the next higher lamp in the tier — a blue one — flashes on. At twenty comes a green light, at twenty-five a clear white light, and at thirty miles an hour or more a

��red signal shows. Never more than one lamp is lit at any given time, except in the case of a car which has exceeded thirty-five miles an hour. At this point the red light short-circuits, and stays burning even though the car slackens speed or stops. If a car, therefore, shows a red light and a green light at the same time, it means that the car has been going at a rate higher than thirty-five miles an hour, and is traveling at about twenty.

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