Page:A Letter on the Subject of the Cause (1797).djvu/37

 the preſſure of the atmoſphere is now employed in common Fire Engines.”

On reading this paragraph, every perſon acquainted with Newcomen will naturally aſk; How can the expanſive force of ſteam be applied to preſs down the piſton in the manner it is now performed by the atmoſphere, which requires the top of the cylinder to be kept open? For ſuppoſe ſteam to be poured on to the top of it inſtead of air, where is there any footing or butment for the re-action of this expanſive element? I clearly perceive, ſays the enquirer, that the air performs this office by its gravitating power, which requires no butment. But how can any expanſive force be employed without it; ſince it is a law of nature that no force of this kind can be exerted, without being firſt prevented from expanding in the contrary; or at any rate without having a reſiſtance in all directions, equal at leaſt to the force of action required?

Theſe reflections, I conceive, would induce a concluſion, that the man who propoſed ſuch a thing muſt be either a fool or a madman. But to return: On