Air, that would be more than fufficient to make the ne- 
celTary Rarefa£tioii in the Receptacles : And thus much 
might anfwer Mr. Nuis his Objeftion. 
But for the good fuccefs of the Engine it is not enough 
to make the Air pafs from the Receptacles into the Pumps, 
it muft alio return from the Pumps into the Receptacles : 
Now for this intent it would be necelTary to fet the Re- 
cepticles but five Foot above one another ; fb to drive the 
Water up the Pipe NO^ it would be enough that the Air 
in the Receptacle B lliould prels with a ftrength equivalent 
to 23 Foot of Water; For it is plain that 5 Foot in the 
Pipe 0, together with a prelTure equivalent to 1 7 Foot 
which I have fuppofed to be in the upper Receptacle 
will make but 22 Foot in all : and therefore 2 j Foot pret 
fing in the Receptacle B muft prevail and caufe the Wa- 
ter to afcend ; now the prelTure in the Receptacle being 
but 23 Foot, and the Air in the Pump returning to its or- 
dinary prelTure, which is aoout 33 Foot; it is plain that the 
Air going back to the Receptacle will be driven by a 
ftrength equivalent to 10 Foot, as well as it had been in 
coming from the Receptacle towards the Pump: and fb 
the bignefs afligned for the communication-Pipes will alio 
prove more than fufficient to this effeft. 
From what I have been laying it is plain, that in great 
diftances there iliould be made as many Pumps as Recep- 
tacles, as I had propounded in the firft explication of my 
Engine: and for to raife Water but 6 3 Foot high, there 
lliould be required 13 or 14 Receptacles and as many 
Pumps of the bignels aforelaid. SDme people may take 
this for a great difficulty. But I aniwer that in this Engine 
this is not fo much as it feems at firft ; becaule the prel^ 
fare being all from without, there is no need of any great 
ftrength to refift it, and fo the Metal for the Pumps will 
coft but little; there may alfo be found occafions where to 
make fb good ufe of them, that fuch an Engine as I have 
defcribed would in a years time lave labour enough to pay 
