_Answer._ The power is applied to the brakes of the cars in this system by exhausting instead of compressing the air. This is done by means of an ejector, of which fig. 224 is a section. This operates somewhat like an injector. Steam is admitted into the pipe _B_, and escapes through the annular or circular opening _a a_. The effect of this is to create what is called an “induced current,” or to draw the air from the pipe _C′ C_, which, with the steam, escapes at _A_. This produces a partial vacuum in the pipe _C_, which extends back under the cars. The pipes under the cars are connected together by rubber hose, which are prevented from collapsing by coils of wire inside. Under the tender and under each car are India rubber cylinders with cast iron ends, one fastened to the car and the other movable. The rubber cylinders can be extended or compressed somewhat like the bellows of an accordeon. The rubber is supported by iron rings inside, placed from 4 to 6 inches apart, so as to prevent them from collapsing when the air is exhausted from them. When this is done the pressure on the movable cast iron end draws it towards the fixed one, and by attaching the former to the brake levers by a rod, the force of the pressure on the head is communicated to the brakes. The ejector is placed on top of the boiler, and when the brakes are to be applied the locomotive runner opens a valve, which admits steam into the ejector, which instantly begins to produce a partial vacuum and thus apply the brakes. When the pressure of the brakes is to be released, the release valve, _D_, is opened, which admits air into the pipe, _C_, through which it is conducted back to each of the India rubber cylinders, and thus counteracts the pressure on the ends and releases the brakes. Both the atmospheric and the vacuum brakes have recently been applied to the driving-wheels of locomotives with very excellent results. PART XXIV. PERFORMANCE AND COST OF OPERATING LOCOMOTIVES. QUESTION 445. _What is the cost of operating ordinary locomotives per mile run?_ _Answer._ The average cost at the present time (1874) is from 20 to 25 cents per mile.[103] [103] Deducting 10 per cent. from this amount will give very nearly the gold value of the cost. The figures given above represent the cost in the depreciated promises to pay of the United States Government. QUESTION 446. _What items of cost are included in this, and what proportion do they each bear to the total cost?_ _Answer._ The items of cost and the percentage of each to the whole expense of operating locomotives, and also to the total of all the expenses of operating locomotives are given in the following table: