171 the Constructlov of Stcam-Evgines. 34 1 



muuicate with each other, that they may at one and the 

 same time receive and part with the steam by which the 

 engine is worked ; and their respective piston rods are so 

 connected with one another, or with other parts of the 

 machinery, that the pistons may act together. 



3dly. With regard to steam-engines wliich are alreadv 

 constructed, I improve the same by adding thereto a small 

 cvlindcr o^- measure for the steam admitted to the working 

 cylinder: this improvement may be introduced with great 

 advantage into the steam-engines constructed according to 

 Mr. Watt's improvements ; which small cylinder may be 

 'either employed only as a measure of the steam, or a piston 

 may be worked in it by the expansive force of the steam, 

 before it be allowed to pass into the present working cy- 

 linder or steam-vessel, which in that case must have no 

 direct communication with the boiler, but must be supplied 

 with steam through the medium of the small added cylinder 

 or steam measure. To make this more intelligible, suppose 

 the steam measure or small cylinder added to one of Mr. 

 Watt's single engines, or to one of similar construc- 

 tion, and that the small added cylinder is furnished with 

 a piston to work by the expansive force of the steam, 

 while the larger cylinder works by condensation ; then all 

 that is necessary is, that the top of the smaller added cy- 

 linder be connected with the boiler, and furnished with a 

 cock or valve to shut off the steam, and that the boiler be of 

 sufficient strength : let a pipe pass from the top to the bot- 

 tom of tlie smaller added cvlindcr, furnished with a cock or 

 valve, bv which a communication may be riiade between 

 the two sides of the piston in the said cylinder; let a pipe 

 also pass from the bottom of the smaller cvlinder to the top 

 of the larger; let the larger cylinder, as is now commonly 

 the case in practice, have a pipe passing from its top to its 

 bottom, by which a communication can be made between 

 the two sides of the piston in the large cylinder ; and let 

 the large cylinder communicate with a condensing-vessel, 

 with valves, cocks, or anv other contrivance to open or 

 .shut the different communications when necessary. Things 

 being tims arranged, suppose the engine at work, and the 

 pistons in hot!) cylinders at the top of their respective cy- 

 linders, and suppose the steam admitted to enter the small 

 cylinder above the piston : while the steam is thus enter- 

 ing, let the communication between the bcttom of the 

 small cylinder and the top of the large one be open, while 

 the bottom of the large one is open to the condenser ; then 

 both pistons will descend. When they have reached the 

 Y 3 bottom 



