r *43 8 ] 
fhut the injection ; fet open the cock at V, that the 
air may be difcharged by the entrance of the fleam 
into the receiver. This being done, fliut that cock, 
and let go the arm ; the weight W will bring over the 
balance to the left, and in its motion fhut the fleam- 
cock, and open the injection ; this prcfently condenfing 
the fleam into water, in a great meafure leaves a 
' vacuum in the receiver. Things remain in this fitu- 
ation, till the preffure of the atmofphere has caufed 
the water to mount thro’ the fuction-pipe into the re- 
ceiver, where, as its furface rifcs, it caules the float to 
afcend 5 and, deprefling the arm AB , raifes the ba- 
lance, till it has palled the perpendicular; and, in its 
defcent, which is done by its own gravity, the roller K 
lays hold of the arm R S, again opens the fleam-cock, 
and fhuts the injection. The receiver being now al- 
mofl filled with water, the balance cannot return, till 
the furface of the water therein fubfides, and fuffers 
the float to defcend. This is performed by the elafti— 
city of the fleam ; which, at the fame time that it fills 
the receiver, drives out the water thro’ the forcing- 
pipe ; and when the furface is defcended fo low, as to 
fuffer the weight W to bring the balance beyond the 
perpendicular towards the left; it then falls of its own 
accord, and, in falling, the roller I lays hold of the arm 
R S, fhuts the fleam-cock, and opens the injection, as 
before. 
When the engine is defired to be flopp’d, obferve, 
when the balance lies to the right, to turn round the 
arm O m of the injection-cock, fo that the tail of the 
fleam-cock may mifs it in the next motion ; fo that, at 
the fame time that the receiver is fill’d with fleam, and 
the fleam- cock fliut, the injection not being opened, 
the motion will flop for want thereof. 
LXXIII. 
