After the locomotive had been in active service about 20 years there was a demand for built and experimented with in these early years.
The names of Stephenson, Baldwin and Brooks appear in the following list of early locomotives. Their work is known to all in terested in locomotive equipment and their work is largely responsible for the magnificent locomotives we see running to-day.
higher speed. Heretofore the speed was very moderate. To secure the higher speed the drivers were increased to seven feet in diameter, but they were soon discarded as the locomotive was slow in getting up speed. The time had not arrived, however, for high speed in railroad travel: As yet there were no fixed signals, no air brakes nor reliable systems for regulating single track operation. The appli cation of the air brake in 1873 paved the way for our modern freight and passenger service. For a time the early builders of locomotives believed that there was not sufficient adhesion between the wheels and the track to climb an incline or draw loads. The tractive effort of any locomotive is reached when the driving wheels begin to slip. To increase this limit a definite part of the total weight was carried on the drivers to give the desired adhesion. Another method was to drive separately the individual pairs of drivers. The load on one pair of drivers was limited, however, to the load the right of way would bear with safety. This fact brought into use leading trucks or "bogies* and trailing trucks which received a Since 1904 the Walschaert, valve gear in vented in 1844 by a Swiss named Egide Wal schaert and used quite extensively in con tinental Europe has increased in favor among locomotive builders and is now used to a greater extent in this country. In modern loco motives the use of an outside valve gear such portion of the weight of the locomotive. An arrangement of this kind increased the wheel base considerable and additional provisions had to be made to enable the locomotive to run around curves. Lateral play was allowed the axles, radial axles were used, axle trucks turn ing about a pivot which receives a portion of the weight were also used.
Many forms of valve gears were applied to the earlier locomotives. "Old Ironsides* is equipped with what is known as "the Hook Motion.* This gear was the standard form used in this country for some. time even after the invention of the shifting link.
"The Hook Motion" was replaced by the Stephenson link mechanism invented in 1843 by William Howe, an employee of the Robert Stephenson & Company of New Castle, Eng land. Up to 1904 practically all the locomotives as the Walschaert is practically necessary, be cause of the increase in size of our locomotives. In the large locomotive the parts of the Stephenson mechanism are very large, thus per mitting rapid wear and the accumulation of a great amount of lost motion. The Wal schaert valve gear has no eccentrics, only pins, links and bushings. It is easily accessible and maintained. Using a valve gear outside of the frame also permitted better frame bracing and thus reduced the chance of frame failure.
During the last 25 years many improve ments have been made. These have led to the superb locomotives now running in Europe and America. Many investigations have been made relative to increased boiler pressures, 'com pounding, use of superheated steam and pre vention of smoke, all of which have been of inestimable value.
in the United States were equipped with this gear. The gear is located between the drivers and provides a means of reversing the engine at will and also permits the volume of steam admitted to the cylinders to be varied by the operator while the engine is running.
The Locomotive of To-day.— The loco motive might be dealt with as a power plant complete in itself, consisting of boiler, fur nace, stack, engine and auxiliaries. It will de velop the same amount of power as a station ary power plant occupying several times the amount of space. Modern locomotives are built as high as 3,000 horse power, with a tractive effort of 105,000 pounds. Comparing the econ omy of the modern locomotive with the loco motive of 20 years ago it will be found that in many cases 50 per cent more work is obtained per pound of coal burned.