Page:A Letter on the Subject of the Cause (1797).djvu/51

 that which is conſtantly preſerved above the mercury in the leg or tube of the barometer; will not this tube be exactly the leg or eduction pipe propoſed by Mr. Gitty, with this difference only, that in one is uſed water to balance and exclude the outer air, and in the other mercury? Conſider the vacuum of the condenſer to be uniformly maintained, will there be any other cauſe to move the water in the eduction pipe, but that which gives motion to the mercury in the barometer? I anſwer no; if the water in this pipe is either elevated or depreſſed, it muſt be by the varied efforts of the outward air to enter the vacuum above. Thus none of this water can poſſibly be diſcharged below a balance to the atmoſphere, was the pipe continued down a thouſand, or any greater number of feet. Having prepared your LorſhipLordſhip [sic] for the proof I will produce it.

It will be neceſſary to keep in remembrance, the eduction pipe of Mr. Watt’s Engine, which is placed above this condenſer, communicates and forms a junction with this vacuum, and into which falls all the condenſed water and uncondenſed vapour, every ſtroke the Engine makes. Now ſuppoſe that water enters firſt, or