Page:A Letter on the Subject of the Cause (1797).djvu/38

 On conſidering the ſtrange difference I ſaw in this machine from that of Newcomen, I concluded in my own mind the following to be the real invention of Mr. Watt in the cylinder part of the Engine. Firſt. He has completely inverted the order of Newcomen, by turning the cylinder upſide down. Secondly. By making the proper inlets and outlets for the ſteam, at the upper, inſtead of the lower end of the cylinder.

Thirdly. The valves uſed in theſe inlets and outlets for the purpoſe of admitting and ſhutting off the ſteam; and for retaining it in the cylinder and diſcharging it; and the manner of giving motion to them from without, are very peculiarly and curiouſly contrived; and totally different from any article ever applied in Newcomen’s Engines for the ſame purpoſes. And theſe valves, &c. I obſerve are made always of braſs, or a mixture of copper and braſs; and I cannot ſee of what other metal ſuch very eſſential parts could be made; as iron would ſoon ruſt, and in a few weeks loſe the perfection requiſite to keep them air and ſteam tight.

Fourthly. I caſt my eye on a ſingle part where depends the whole effects of the Engine; and which part not being properly accompliſhed would