Popular Science Monthly 169 



Storage batteries are A Tell -Tale Light System— First Assist- 

 ant to the Motorcycle Cop 



of 



quick succession. 



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. 



