CATALOGUE OF THE MECHANICAL ENGINEERING COLLECTION, 69 



a pair of eccentrics fixed to a loose sleeve wbicli couUl be moved endwise along 

 the shaft by a pedal so as to engage with eitlier of two drivers, one set for 

 forward and the otlier for backward running. The valve rods had gab ends, 

 so that the valves could be disengaged and worked by hand levers when 

 reversing. The crank pins had spherical ends to allow for irregular motion of 

 the engine relative to the driving axle. 



The boiler was a cylindrical shell 40 inches in diameter by 6 feet long, 

 made in two rings, witli a circumferential lap joint and longitudinal butt 

 .ioints, the flat ends being secured by angle rings and tied together by longi- 

 tudinal stays. The shell was traversed by 25 copper tubes 3 inches in diameter 

 secured in holes through the end plates. The fire box shown is of the original 

 design, but it is not certain how soon it was altered in shape. It was a sepa- 

 rate chamber of copper bolted on to the back end of the barrel. It was rect- 

 angular in plan, with a sloping back, in which was the fire box. There were 

 water spaces at the top, back, and sides, while there was a fire-brick lining in 

 front below the tubes. Copper pipes connected the water and steam spaces 

 of the fire box with those of the barrel. The total heating surface of the 

 boiler was 138 square feet, that of the fire box being 20 square feet, and the 

 grate area was 6 square feet. The chimney was nearly 15 feet high above 

 the rails and was swelled out at the base to cover the tube ends, and was 

 supported by stays from the cylinder plates. 



Steam from the boiler was admitted to the cylinders by two pipes leading 

 from a regulating cock fixed above the fire box, and which received steam from 

 a dome through an internal pipe. The boiler pressure was limited to 50 pounds 

 per square inch by two safety valves, one of which was loaded by a spring and 

 lever, while the other was a lock-up valve covered by a small dome. A mer- 

 curial gauge was fitted beside the chimney and was arranged to indicate the 

 steam pressure from 45 to 60 pounds. A water gauge was fitted behind one 

 of the cylinders and two gauge cocks near the front end of the boiler. The feed 

 water was introduced by a long stroke feed pump worked from one crosshead, 

 while the exhaust steam was passed into the chimney by two pipes, each 

 fitted with a brass nozzle 1.5 inches in diameter. 



The framing of the engine was wholly between the wheels and was built of 

 flat bar iron bent down at the rear end to accommodate the fire box and rear 

 axle ; to this the cast-iron guides were secured, and four brackets to support 

 the boiler. The weight was transmitted to the axles by plate springs. The 

 driving wheels were constructed with cast-iron bosses in which the crank pins 

 were fixed, oaken spokes and fellies, and iron tires secured by bolts. The 

 engine weighed 3.25 tons when empty and 4.25 tons in working order. 



The tender was a four-wheeled wooden truck carrying the fuel in the body 

 and the water in a large barrel above it. The axles had outside bearings and 

 plate springs, the wheels were 36 inches in diameter and the wheel base was 

 4 feet. It weighed 3.2 tons when loaded, so that the total weight of engine and 

 tender in working order was 7.45 tons. Cat. No. 180,243 U.S.N.M. 



Model of John Stevens Experimental Locomotive, 1825. Made in the 



Museum. 



The locomotive consists of a four-wheel platform truck upon which 

 is mounted a vertical tubular boiler inclosed in a circular sheet-iron 

 casing" terminating in a conical hood that holds the furnace door. 



