Page:A Letter on the Subject of the Cause (1797).djvu/95

 There is a proper ratio or maxim to be given, for determining the ſize of the pump for each Engine; and ſhould there be any deviation from it, either over or under, the Engine is not perfect.

The want of proportion in theſe parts for many years occaſioned very great defects, and even prevented, in toto, the uſe of Mr. Watt’s Engines; and they are ſtill incomplete on this account.

Newcomen’s Engine is the beſt yet known, that works without an air pump.

Newcomen’s Engine, with a proper air pump, will far exceed any yet known in public uſe, in point of ſimplicity; and, at leaſt, equal or ſuperior in power with the ſame quantity of fire; and can be built and maintained at little more than half the coſt of Mr. Watt’s.

No condenſer or edudction-pipe of any dimenſions, whatever, is neceſſary in Engines built on this plan. The judicious application of an air pump will make every Stream Engine a good one, but this the beſt. Theſe