44© Air. cavallo’s Defcriftion of 
pais through collars of leathers held in proper bra fs boxes HQ^, 
fcrewed to the piece K, and furnifhed with caps, n, 1 1. The 
lower extremities of the wires are fattened to the crofs bar, 7, 7, 
of the brafs frame, OOO, a vertical view of which is (hewn 
in fig. 4. of plate II. 
From the middle of the piece L, fig. 1. pi. III. a pillar M 
proceeds, the lower part of which, branching into two horizon- 
tally, forms an axis z, z, fig. 4. pi. II. about which the brafs 
frame OOO moves a little way upwards and downwards. 
It appears from this defcription, that if the frame OOO fig. 4. 
pi. 111. is moved upwards, the wires 9, 9, and likewife the double 
ling 8, 8, with the oil- filk, being all connected together, will be 
pufhed alfo upwards ; confequently, the oil-filk being removed 
from the hole of the piece K, a free communication is opened 
between the cavity of the tube R, and the cavity of the barrel, 
through which the air, however rarefied or weakened in elafti- 
city, can pafs without the lead impediment. 
In order to move the brafs frame upwards, the end of a lever 
P bears again ft it. This lever is fihewn in fig. 3. of plate Ik 
which is a front view of part of the pump, whereas fig. 1. of 
the fame plate is a fide view of it. The center of motion of 
the lever is at 13, that is, between two fide prominences of 
the piece 12, 12, which is faftened by ferews to one of the 
wooden pillars of the frame of the machine. The part 1 4 of 
the lever, which projects beyond the wooden pillar, is made 
with a joint, by which means it may be turned upwards, as 
reprefented by 17, for packing it more conveniently. 
When the valve is to be opened, the foot oi the operator 
muft prels upon the extremity 15 of the lever, by which means 
the other extremity P, the frame OOO, the wires 9, 9, and 
tiie double ring 8,8, with the oil-filk, are all lifted up. But in 
order 
