; C J 9 8 ] 
It is evident, in the firft place, from a fundamen- 
tal law of mechanics, that, the content of the cylin- 
der remaining the fame, the quantity of water dif- 
charged at each lift will in all cafes be equal, by only 
changing the diftance of the center of the pifton from 
the fulcrum of the balance. You will agree like- 
wile (for I fuppofe the principles and working -part 
to want no defcription) that the excefs of the pillar 
of atmofphere above that of the water is a weight on 
the pifton, driving it to a depth of five feet, or there- 
about, by the prefent conftruCtion, withfcthe cavity 
of the cylinder; acceleratedly till friction and an im- 
pediment from the fleam, which remains in the cy- 
linder even after the jet d’eau, and is increafcd in 
elafticity, whilftits bounds are dimimfh’d, fhall equal 
the accelerative force ; and that then again the pifton 
is retarded the reft of the way. It may be convenient 
to remark too, that if the rarefaction be fo complete, 
that the defcent wouid be greater than the conftruc- 
tion admits of, the retardation is augmented by a 
brachium of the balance prtfling upon fprings. But 
to fay nothing of friction here, we can, notwith- 
ftanding this diminution of force by the remainder 
of fteam within the cavity of the cylinder, demon- 
ftrate the ratio of the velocities, and the times of 
defcent of the piftons, in cylinders of unequal alti- 
tudes, to be exaClly the fame, as if the refiftance 
was nothing; whence we fhall without difficulty ar- 
rive at fome conclufion in this matter. 
MN is the working-part of a fteam-engine cylin- 
der, of the ufual height, equal in diameter to a 
ffiorter one m n ; and the rarefaction in both of 
them being fuppofed the fame, 
and 
V 
