Hundreds of lives may depend upon prompt action, thousands of dollars' worth of property are in the engineer's hands, either to waste or save when the moment of the break down comes. In Mr. S. A. Alexander's excellent treatise entitled "Broke Down" is placed in red letters over every page, "Protect Yourself from Approaching Trains." When a break-down occurs, this is the first thought which should enter the engineer's mind, and the first act should be to carry it out. There are many causes of a break-down, too many to enumerate. In the roundhouse is the place to study break-downs, for here, daily, every variety is open to inspection--broken crank-shafts, broken eccentric-rods, eccentric-straps and sheaves, broken motion and broken springs. Of course an engine may be broken, and yet able to run its train through. This is an important consideration. Some engineers hardly know when they are beaten. It is a matter of record that a certain engineer, known as "Hell-fire Jack," ran his train over a bridge after one side had been washed away by a raging flood. Thousands of such daring deeds have been accomplished by engineers, but "Cautious Jacks" will be better appreciated by the company than "Hell-fire Jacks" every time. Real heroism lies in good judgment and a cool head. Suppose that the right hand back gear eccentric-rod breaks. "Can I get along in forward gear, after having disconnected the rod and the strap?" is the question. The answer is yes, and it should be prompt, as all such answers should be when the engine breaks down. It is such readiness as this that makes break-downs but a matter of a few moments. It is also highly necessary that the engineer should ask himself "What tools have I upon the engine? What can I do with them? Can I find them in the dark? If I run off the track in what condition is my screw jack? Will it work properly? Have I a ratchet or bar to work it with?" These are things which should be continually kept in mind. AIR BRAKES. The air-brake has changed engine driving materially in the last few years, and a word or two concerning it should be said. The air-brake consists briefly of an air cylinder placed beneath each car, which can be operated by the engineer from the foot plate, the pressure of the air controlling the action of the brakes. There are two valves to an air-brake, one for ordinary stops and the other for sudden stops in case of emergency. In the first only partial pressure of the confined air is used, in the latter the full pressure is employed and the brakes brought against the wheels with all force at once. One of the most important duties of an engineer is to be well assured that the air-brakes are in proper working order. After the call for hand brakes has been given, the air brakes must not be applied until the hand brakes are released. Air and hand brakes should never be used at the same time on a car.