CONTIJ^ UO US BAIL WA Y BRAKES. 37 



suits applies equally in its degree to the higher speed stops, as it will be ob- 

 served that the relative efficiencies of the Vacuum brake to the Automatic 

 vary but little independent of speed. The time occupied is here|nearly half 

 as long again, as is also the distance run. The total foot-tons of energy in 

 the Vacuum train are rather greater than in the Westino;house, although 

 the speed of the latter is somewhat higher. The efficiency of the Westing- 

 house brake, as compared with the Vacuum, is, however, much higher, even' 

 when both are in full work, while the latter is not in operation in reducing 

 the speed until some considerable distance has been run after the moment of 

 application. Thus, in the diagrams we are just now considering, it will be 

 observed that the speed of the Vacuum train was unaifected at a distance of 

 100 ft.' after application of brakes, and when the Westinghouse had already 

 done more than 5 per cent, of its work by reducing the irain speed from 30 

 to 28.5 miles per hour. This distance is much more marked at the end of 

 the third 100 ft., when the speeds stand 23.15 and 13 respectively, and the 

 train energies at 3216 and 938 tons, so that the values of the two brakes at 

 this point as regards speeds are in the proportion of 1.77 to 1, and as re- 

 gards train energy destroyed 3.4 to 1. In other words, when the Automatic 

 brake had performed its work, the Vacuum train was still traveling- at a 

 relatively high rate of speed. This result is, of course, more striking, in the 

 higher velocity stops. Thus in one of the three trials at 40 miles per hour, 

 the speeds at 500 ft. from application of brake (Test No. 2) are 32.5 and 16.5 

 respectively, or almost exactly 2 to 1, while the foot-tons of energy are in 

 the ratio of 4 to 1. In other experiments this is far more strongly marked, 

 as in the trials 12 S. V. and 12 W. A. (Test No. 4), where the speeds were in 

 each case 54 miles an hour. In these, at the end of 900 ft., the speeds are 

 38.25 and 7 respectively, or 5^ to 1, while the foot-tons of energy were 8400 

 against 270. The Vacuum train was thus proceeding at a rate of over 38 

 miles an hour, or faster than the train which was wrecked at Arlsey Siding 

 the other day, after the Automatic train was at rest. Of course, it is in these 

 stops at the highest speeds that the qualities of the two brakes manifest 

 themselves; they have more work to do, and as they require a longer time 

 in which to do it, they afford better opportunities for analysis. Thus taking 

 runs 11 S. V. and W. A. (Test No. 5), at 55 miles an hour, we find that the 

 time required for the former is one-third greater than for the latter, and the 

 distance run 50 per cent, greater. In these particular tests an interesting 

 point occurs, which manifests itself on the diagram. The Westinghouse 

 brake was not applied until a brief interval after the diagram was com- 

 menced. The consequence was that while the Vacuum train was lessened 

 in speed 45 per cent., the Westinghouse train remained almost at its normal 

 velocity. But during the second 100 ft. the Westiughouse performed 7.27 

 per cent, of its work against 1.82 per cent, of the Vacuum train, and it is 

 only until 400 ft. are passed that the Vacuum brake approaches its full per- 

 formance, which, however, is not reached till after the Automatic brake has 

 arrested the train. In fact, the whole of these trials clearly show the dis- 

 advantages inherent to the Vacuum system, which we have consistently 

 pointed out— an unavoidable slowness in action at the moment when the 

 promptest application possible is required. The somewhat interesting 

 comparison that these trials render practicable between the detailed per- 

 formances of the two systems, and a theoretically perfect stop, we shall have 

 to defer till another occasion, remarking only meantime that while the 

 Westinghouse Automatic shows an average percentage of absolute efficiency 

 of about 65, the Vacuum falls to 30, while taking the absolute thoretical 

 distance that must be run in making a stop, the ratios are about as 70 to 50. 

 "The tables and diagrams which record the whole results of the trials 



