20 BULLETIX 119, U. S. XATIOXAL MUSEUM. 



Print from a Model in South Kensington Museum of James Watt's Double- 

 Acting Beam Engine. Patented, 1782. 



In this engine the chain heretofore connecting the piston rod to 

 the beam is discarded and a parallel motion substituted, enabling the 

 piston to push as well as pull the beam. The engine is also double- 

 acting, the steam and vacuum operating from opposite sides of the 

 piston at the same time, both in the same direction, then both are 

 reversed and the piston forced the other way. 



Cat. No. 180,625 U.S.N.M. 



Print of James Watt's Semirotary and Rotary Engine. Patented, 1782. 



Three Views. 



The semirotary engine has a piston fixed in a radial line to the 

 shaft to be turned, and the cylinder fits the piston as it moves back- 

 ward and forward through a considerable arc of the circle; fixed 

 inside the cylinder at one part is a fixed stop or cylinder bottom for 

 the steam to act against either way, as it acts against the piston in 

 either one direction or the other. It was intended to let the recipro- 

 cating shaft act with a spur wheel on two racks attached to the pump 

 rods. There was an unfinished model of this engine in the "Wati 

 Room " at Heatlifield Hall, England, no doubt made partly by Watt's 

 own hands. In a letter of Watt, dated 27 September, 1782, he speaks 

 of this model as having been made so far in 1765 or 1766. 



The rotary engine has a piston fixed as an arm, and a radial line to 

 the shaft to be turned. The cylinder of the engine fits the piston 

 in its revolution, there being at one point a flap valve hinged to the 

 inside of the cylinder, whilst its other end rests on the shaft so as 

 to form a cylinder bottom or point of contact for the steam to act 

 against when acting also against the piston. This flap valve is at a 

 slight angle to a radial line, so that when the piston comes around 

 it can heave it up so as to get past. Cat. No. 180,621 U.S.N.M. 



Print from a Model in South Kensington Museum of James Watt's Bull 

 Engine. Patented, 1782. Two Views. 



This engine is supposed to take its name from an engineer by the 

 name of Bull, who put up some engines in Cornwall. It is peculiar 

 in that the piston rod passes out at the bottom of the cylinder through 

 a stuffing box, the beam being placed below. 



Cat. No. 180,626 U.S.N.M. 



Print of a Single-Acting Engine With a Balance Weight. Made According 

 to James Watt's Patent, 1781. 



The engine is single-acting and has an open-top cylinder, with air 

 pump, condenser, and heavy balance weight on the connecting rod to 



