FIFTY YEARS OF MECHANICAL ENGINEERING. 535 



will exert the greatest power as yet secured from one cylinder. The 

 stroke is fourteen feet and the diameter of the cylinder is nine feet 

 two inches, and the engine is expected to develop eight thousand horse- 

 power. As an illustration of the size of the engine, the wrist-pin is 

 almost exactly the size of a flour-barrel. 



We now come to the engines and boilers used for railways. The 

 year 1832 was the beginning of our present passenger and railway 

 system on this side of the water, and, if the engines imported in that 

 year to run on American roads are any indication of the state of the 

 science of steam-engineering abroad, they could not have been much 

 in advance. At this time the engine and boiler weighed about eight 

 tons, carried forty pounds pressure, and could make about twenty 

 miles an hour under light load and favorable conditions. The engine 

 of that date could not pull more than three or four times its own 

 weight, and had to stop at stations to fill boilers, as they could not 

 pump while running. 



The speed to-day is from forty to sixty miles an hour, and the en- 

 gines weigh from thirty-five to eighty tons, and draw as high as eight 

 hundred tons of paying freight in addition to the weight of the train. 

 To-day the pressures run from one hundred and thirty-five to two hun- 

 dred pounds. The latter pressure is used in Switzerland. The auto- 

 matic and continuous breaks now stop a heavy train within four hun- 

 dred yards at a speed of sixty miles an hour. Recent trials show that 

 these breaks will absorb twenty miles of speed in one minute. 



In 1832 the transmission of power was by flat tumbling-rods and 

 cast-iron shafting of great weight and little strength. To-day we have 

 smooth, light, rapidly revolving steel or iron shafting, supplemented 

 and aided with rubber and leather belting where the latter will serve 

 and the former can not. Where power has to be transmitted at a great 

 distance, wire ropes, moving at a high rate of speed, are used. Wire- 

 rope transmission commences at the point where the belt and shafting 

 become too long or heavy to be useful. It is much cheaper than its 

 equivalent of shafting or belting. In fact, a long line of shafting 

 would cost more for oil in a year than a wire rope would in fifteen. 



At the Rhine-fall, in Switzerland, eight hundred horse-power is 

 transmitted a distance of two miles to a village where fifty small 

 manufacturing industries, situated in every conceivable position rela- 

 tive to the cable-line, secure power. For ten years the cable street- 

 railway system has been in use in San Francisco. The same system,, 

 slightly modified, is being adopted in many Eastern cities. 



Fifty years ago compressed air had not been successfully employed 

 in engineering, though its application as a blast to forges is coextant 

 with history. Sir Henry Bessemer's steel process was made possible 

 only upon the ability of engineers to furnish air under pressure in the 

 converter. The importance of compressed air and the part it has 

 taken in recent engineering undertakings can not be overestimated. 



