44’2T‘ Mr. cavallo’s Defcription of 
undejrftood by infpedting the figure, than by a verbal defcription, 
which piece confines the round leathers from itfelf to the plate r, 
and alfo from itfelf to the other plate, which is fcrewed upon 
the axis at K. 
Between the Lift mentioned plate and the cap F, there is a 
fpiral fteel fpring, which always pufhes the piflon upwards. 
Lafily, the axis of the pifton is perforated from its top till 
towards the middle, where the perforation, opening fide-way, 
communicates with the cavity of the tube I I. 
Now, when the pifton is pufhed upwards, as it always is 
when the extremity O of the lever is not prefled down, then 
the oil-filk at LL, laying againft the plate r, covers the hole 
of the pifton, confequently it flints the communication be- 
tween the barrel and the cavity of the tube H, &c. But if 
this communication is required to be opened, then the extre- 
mity O of the lever is prefled down, which will feparate the 
upper part of the pifton from the contact of the oil-filk, fo as 
to open the communication as required. 
Let us now return to the defcription of the other parts of the 
machine, as fliewn in fig. i. The upper extremity o of the 
tube RS is made conical, and is fitted by grinding into the 
ftrong brafs piece of communication UX/; the cap T ferving 
to tighten it*. The extremity n of the oppofite piece np is 
likewife fitted by grinding into the part /, and is tightened by 
the cap m. Juft over the faid conical extremities n and o, and 
into the fame piece of communication UX/, are adapted two 
flop-cocks Z and h , which are tightened down by the caps 
* All the parts of this pump, that are fitted to each other by grinding, as the 
ftop-cocks, the extremity of the tube RS, See. before they are put together, arc 
imeared with a mixture of bees-wax and oii melted together, in order to let them 
flop the better, and to prevent their wearing by friction. 
Y and 
