There is not space here to enter into the history of the air-brake. It was first practically applied to passenger trains in 1868. The first great epoch in its subsequent development was the invention, by Mr. George Westinghouse, Jr., of the triple valve. The introduction of the triple valve at once reduced the time of full application of the brake for a ten-car train from twenty-five seconds to about eight seconds. This means, at forty miles an hour, a reduction by more than one thousand feet in the distance in which a train can be stopped. The next great epoch in the history of the air-brake was made by the celebrated Burlington brake-trials of 1886 and 1887. These trials were undertaken by a committee of the Master Car-builders' Association, to determine whether or not there was any power-brake fit for freight service. For general freight service the brake must be capable of arresting a very long train, with cars loosely coupled, running at a fair average passenger speed, without producing objectionable shocks in the rear of the train. The two series of trials were carried out in July, 1886, and May, 1887. The competing brake-companies brought to the trials trains of fifty cars each, equipped with their devices. Skilled mechanical engineers from various railroad and private companies assisted both years. These trials were most exhaustive, and have contributed more to the art of braking than any that preceded or have followed them. The first year's trials developed the fact that the air-brakes could not be applied on the rear of a fifty-car train in less than eighteen seconds, whereas the head of a train moving twenty miles an hour could be completely stopped in fifteen seconds. The result was that disastrous collisions between the cars of any one train were produced in the act of stopping. Men in the rear cars were thrown down and injured, and much damage was done to the cars. At the end of nineteen days the brake-companies went home to work another year over the new problem. In 1887 they reappeared on the same ground, and in eighteen days proved that no simple air-brakes, as then operated, could prevent disastrous shocks in a long train; but it was shown that by bringing in electricity to actuate the air-valves, the application of the brakes could be made practically simultaneous throughout the train. Mr. Westinghouse, however, during the summer following, made such modifications in the triple valve and in the train-pipe that he succeeded in applying the brakes throughout a fifty-car train in two seconds. That settled the matter. He at once equipped a train of fifty cars, and in October and November, 1887, that train made a journey of about three thousand miles, making exhibition stops at various cities. The journey was a splendid and conclusive demonstration that the air-brake is now a thoroughly efficient and reliable contrivance for freight as well as for passenger service. The result has been a very rapid application of the new quick-acting brake to freight cars. The performance of this train was to railroad men most impressive. A freight train of fifty cars is about one-third of a mile long. To see such a train, running forty miles an hour, smoothly stopped in one-third of its own length, without shock or fuss, was an object-lesson that no one could fail to understand or to remember. Some of the stops made by this train will give a fair notion of the relative power of hand- and air-brakes for quick stops. The following figures are averages of stops made in six different cities. They give the distances run in feet from the instant of applying the brakes till the train was brought to a stand-still: