Page:Philosophical Transactions - Volume 016.djvu/274

 Air, that would be more than sufficient to make the necessary Rarefaction in the Receptacles: And thus much might answer Mr. Nuis his Objection)

But for the good success of the Engine it is not enough to make the Air pass from the Receptacles into the Pumps, it must also return from the Pumps into the Receptacles: Now for this intent it would be necessary to let the Recepticles but five Foot above one another; so to drive the Water up the Pipe NO, it would be enough that the Air in the Receptacle B should press with a strength equivalent to 23 Foot of Water: For it is plain that 5 Foot in the Pipe NO, together with a pressure equivalent to 17 Foot which I have supposed to be in the upper Receptacle A, will make but 22 Foot in all: and therefore 23 Foot pressing in the Receptacle B must prevail and cause the Water to ascend: now the pressure in the Receptacle being but 23 Foot, and the Air in the Pump returning to its ordinary pressure, which is about 33 Foot; it is plain that the Air going back to the Receptacle will be driven by a strength equivalent to 10 Foot, as well as it had been in coming from the Receptacle towards the Pump: and so the bigness assigned for the communication-Pipes will also prove more than sufficient, to this effect.

From what I have been saying it is plain, that in great distances there should be made as many Pumps as Receptacles, as I had propounded in the first explication of my Engine: and for to raise Water but 6o Foot high, there should be required 13 or 14 Receptacles and as many Pumps of the bigness aforesaid. Some people may take this for a great difficulty. But I answer that in this Engine this is not so much as it seems at first; because the presssure being all from without, there is no need of any great strength to resist it, and so the Metal for the Pumps will cost but little: there may also be found occasions where to make so good use of them, that such an Engine as I have described would in a years time save labour enough. to pay