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The Westinghouse Brake 127 But the lack of control over a breakaway was the greatest danger, which demanded instant attention. Thereupon Mr. Westinghouse once more took up the problem, his goal being the perfection of an automatic system. In consummating this end, in which he was strikingly successful, he was able to profit from another invention which he had evolved, and which had been adopted upon trains. This was a signalling system, comprising a pipe extending beneath the carriages throughout the length of the train to the locomotive, on which was mounted a small cylinder carrying a whistle. If a valve connected to this pipe were opened at any point of the train, the whistle was blown, thereby attracting the driver’s attention to the fact that something was amiss. The success of this signalling device depended essentially upon a very sensitive valve controlling the passage of air from the reservoir upon the engine to the train pipe, and this always came into action whenever any air was permitted to escape from the train pipe through the opening of a signalling valve, say, by the guard or passenger. It was the movement of the delicate valve on the reservoir which brought the whistle into play. As a result of several interesting experiments, from which it was ascertained that waves of air travelled through the signalling pipe at the same velocity as sound, namely 1,100 feet per second, Mr. Westinghouse conceived a brilliant idea. He decided to introduce a valve combination into the braking system, which was still further improved by adding an auxiliary reservoir to the original equip- ment beneath each carriage. The valve system was