30 BULLETIN" 119, U. S. NATIONAL MUSEUM. 



pump and is connected by a link to the middle of an upright lever 

 oscillating on an axis on its lower end and connected by a horizontal 

 connecting rod to the crank. In working steam at the high rates of 

 expansion indispensable to the attainment of the best economic re- 

 sults, there must be applied to the pistons during certain parts of 

 the stroke an amount of steam power largely in excess of that re- 

 quired to overcome the nearly uniform resistance of the water pres- 

 sure on the plungers. As, in the regular operation of the engine, this 

 excess is immediately transmitted to the flywheel to be applied to the 

 plungers before the termination of each stroke, it is important that 

 this transmission of power to and from the flywheel should be at- 

 tended with the least possible loss by friction. The introduction of 

 the upright levers diminishes this loss in an important degree. 



Cat. No. 251,291 U.S.N.M. 



Model of Charles Miller's Rotary Steam Engine, U. S. Patent, No. 23852, 

 May 3, 1859. Transferred from United States Patent Office. 



A two-cylinder engine of the revolving-piston type, the piston 

 being elliptical in shape, with the major axes 90 degrees apart and 

 revolving on a central shaft. Cat. No. 251,292 U.S.N.M. 



Model of James Piatt's Rotary Steam Engine, U. S. Patent, No. 34981, 

 September 15, 1862. Transferred from United States Patent Office. 



The engine is of that type in which the cylinder revolves about a 

 stationary abutment head. Two pistons, one on each side of the 

 abutment, work radially within and rotate with the cylinder. The 

 cylinder is concentric with the shaft and is divided in a plane per- 

 pendicular to the axis of the shaft into two equal parts, secured 

 together about the periphery. One half of the cylinder is secured 

 firmly to the shaft, while the other half is bored centrally much 

 larger and fitted with a stuffing box, through which and into the 

 cylinder passes a stationary sleeve, inclosing the main shaft and 

 carrying the abutment. 



The pistons are parallel sided and are fitted into slots cut through 

 the periphery of the cylinder but inclosed by piston boxes bolted 

 to the outside of the cylinder. The piston rods, which work through 

 stuffing boxes in the piston boxes, have crossheads attached to them 

 to the ends of which are attached guide rods. One guide rod of 

 each piston has attached to it two friction rollers which work on the 

 inside and outside, respectively, of a laterally projecting rim of a 

 stationary cam keyed to the sleeve surrounding the main shaft. 

 This cam holds each piston stationary in relation to the cylinder 

 and in contact with the edge of the abutment durinir half of its 



