exhausted from the collapsing cylinders under the carriages throughout the train. By means of a cord attached to the cam lever in the van, and running the whole length of the train and on to the engine, the driver, or any guard or passenger in the train, had the power of starting the exhauster. In addition to this there was a cord connected with the collapsing cylinders under the carriage, by which any movement in them was made to sound gong-bells in the guards' vans, and close to the driver on the engine. Also by the act of the driver exhausting the air from the collapsing cylinders, by means of the ejectors, the pump-exhausters in the vans are started.

The reports on the working of this break, where it has been practically tried, are generally very satisfactory, and there can be no doubt that it is a far more effective machine than either the chain or the hydraulic break. It however undoubtedly possesses two weak points; the one being the necessity for employing a cord communication to enable the driver to set in motion the break-apparatus in the guards' vans; and the other the employment of rubber sacks and rubber reservoirs, which, though somewhat cheaper in first cost than more durable materials, cannot be maintained as cheaply as iron cylinders and iron reservoirs, and, besides, they must be less reliable, and must at times be more apt to fail as they get old, when they are urgently wanted to act. The slightest cut or puncture would of course detract from their power, if it would not entirely neutralise their use; and this might easily be occasioned, in the event of a part of the train leaving the rails, by sharp stones thrown up from the ballast by the wheels, just when the efficient action. of the break was of the greatest importance.

4. The Air Break.-The Westinghouse automatic air break is the best type of continuous air breaks brought before the Royal Commission. The mechanism of this break and the mode of operating with it may be thus described:A small engine fixed on the locomotive, and deriving its steam direct from the boiler, worked a direct-acting pump, which forced air at pressure into a main reservoir, of nearly 9 cubic feet capacity, placed underneath the foot-plate. Ă line of tubing extended from the main reservoir longitudinally throughout the whole length of the train, with a cock at each end of each carriage. The connections between the carriages were formed of india-rubber hose and metal couplings. Under each vehicle a branch from the main pipe led through a triple valve-of special and complex construction-to a small supplementary air reservoir, and

also to two vertical cylinders provided with pistons fixed under the carriage and on either side of it, midway between the wheels. To the bottom of each cylinder was hung, by a pair of links, two cast-iron cams or quadrants. Each cylinder had a piston, the rod of which passed out through its upper end, and to the top end of this two links were attached. These links were of such form that they passed down the outside of the cylinder. Near their lower ends they were connected with the cams or quadrants just mentioned, and at their extreme lower ends they were connected with the thrust-rods of the cast-iron break-blocks. Thus, when the cylinder piston rises, it draws upwards with it the two links last mentioned, and in doing this the eccentric quadrants roll against each other, forcing the links apart, and, acting on the break-rods, thrust the break-blocks against the wheels. By the reverse of this action the breaks are made to leave the wheels. The breaks on the engine are similar in principle to the carriage-breaks, but the blocks were applied lower down on the wheels, and the arrangement of cylinders and links was somewhat different. There was one cylinder and set of break gear between the two coupled wheels on each side of the engine.

Upon a train being made up, compressed air may be allowed, by opening a three-way cock on the engine, to flow from the main reservoir and charge the whole of the main pipe and all the carriage reservoirs at a uniform pressure. When it is desired to apply the breaks, the compressed air is allowed to escape from the main pipe into the atmosphere through the three-way cock lately mentioned. The reduction of pressure to a small extent by this means operates upon a diaphragm in the triple valve under each carriage, instantly closing a port between the carriage reservoirs and the main reservoir, but permitting, at the same time, the air under pressure to pass from the reservoir to the break cylinders in proportion as the pressure in the main is reduced, thereby applying the breaks. By restoring pressure from the main reservoir to the main pipes the triple valves are shifted so as to charge again the carriage reservoirs, at the same time opening a discharge port in each triple valve by which the air can escape from the break cylinders, and thus release the breaks. The act of breaking asunder the train at any part would have the same effect as allowing the air to escape from the main pipe through the three-way cock on the engine, or through openings provided for the same purpose in the guards' vans or elsewhere.

It is impossible to read through the evidence given.

regarding this break before the Royal Commission without at once coming to the conclusion that in operation, both in this country and in America, its working has been all that could be desired. Besides possessing all the advantages of other continuous breaks, it can claim others which are not common to the latter. By no means an unimportant property of the Westinghouse automatic break is that its normal position is such as to apply the break-blocks to all the wheels of a train, so that the breaks have to be taken off by the driver before starting, and any defect in the mechanism would make itself at once known by the breaks refusing to be taken off in the ordinary manner. Thus infallible evidence is always given on the first starting of a train that the break gear is throughout in working order,matter of no small importance so far as security in travelling is concerned. Another consequence of the automatic action of this break is, that if a train were broken into as many pieces as carriages, each carriage would be stopped by the self-acting application of the break upon its wheels. Also, the break can be applied by the guards as well as by the engine-driver, without the necessity of ropes or other extraneous appliances foreign to the mechanism of the break itself.

A description of the experiments conducted, with the several kinds of break in operation on different railways, by the Royal Commission, is given in Appendix F to their Report. From this some further very important particulars may be obtained relative to the comparative efficiency of the various continuous breaks at present in operation. Besides the general principles of their construction and application, their relative values must depend upon the results obtained from them in actual practice, and in calculating these several considerations must be kept in view; for instance, the speed with which the full force of the break can be applied; the mean retarding forces operating in each case; the distance within which a stop is effected; and the time necessary for taking off the break again-are all subjects of importance which must be taken into account in determining the relative values of different kinds of breaks.

In examining these several points it will not be necessary to review the results of experiments made with ordinary hand-breaks, as they are clearly so insufficient for the requirements of traffic at the present day that they may fairly be left out of consideration altogether. As regards the time occupied in the transmission of break-power through the trains, and in releasing breaks, the conditions under which

the experiments were made did not admit of their being applied to Clarke and Webb's chain break. The observations made of several experiments with each of the other kinds of break gave the following average results :

1. Westinghouse Air Break.-The time occupied in applying the break from the engine to the rear vehicle was from 1 to 1 seconds, whilst the time occupied in taking it off was from 3 to 6 seconds.

2. Smith's Vacuum Break.-The time occupied in applying this break from the engine to the rear vehicle was from 4 to 5 seconds, whilst to take it off required about 24 seconds.

3. Barker's Hydraulic Break.-With this break, if a coupling breaks, the rear portion of the train is placed beyond control of the continuous break, and therefore the report on its operations cannot be given as an average, but must be quoted in detail:

"First trial, from engine to fourteenth carriage, 5 seconds to put on, 8 seconds to take off.

"Second trial, from engine to sixth carriage, 3 seconds to put on.

"Third trial, from engine to fifteenth carriage, not noted, 18 seconds to take off.

"We subsequently severed the train between the eighth and ninth carriages after releasing the flexible pipe, leaving the valves open. When the engine moved on, a cord shut the valves, and the break could easily be applied by driver to the front portion of the train."

After giving particulars of the Westinghouse vacuum and Steele's air breaks, the Report proceeds :-" In these trials the most rapid action, both in putting on and taking off the breaks, was obtained from the Westinghouse air break."

The mean retarding force exercised by the several breaks was tried in a variety of ways, but it will not be necessary to note more than two methods which represented most nearly what would be the case in actual working. In both of these stoppage was ordered by flag signal, upon which all available break or other power was applied by driver and guards to the stopping of the complete train. In the first series of experiments sand was employed, whilst in the latter it was not used.

The following table shows the results obtained with the use of sand;

In the last three cases the total retarding forces were very nearly alike, ranging from 7'79 per cent to 7'47 per cent of the weights of the trains, or within o'16 per cent either way of the mean result. On the other hand, the force. acting on the Midland train with the Westinghouse air break ranged as high as 10'64 per cent, being 3'01 per cent above the mean result obtained by the other breaks. Without the use of sand the results were as follows:

:

London and North Western Clarke and Webb's
Great Northern

It is only necessary to remark here that the Westinghouse air break showed a percentage of retarding force 3'95 per cent above the mean of the results given by the other three breaks.

We have next to consider within what distance a train can be brought to a stand with the several kinds of break above referred to, and it will not unreasonably be concluded that the break which can be applied most expeditiously, and at the same time exercises the highest retarding force, will be found at the head of the list in this case also. The following table gives the distances (approximately) in which the stops would have been effected in each case under the influence of the same retarding forces referred to above, upon the application of break-power to trains running at the speeds of 30, 45, and 60 miles per hour:—