Royal Society.' 443 
exactly the cavity of the cylinder; then let there be a handle 
as N : This engine compounded of all thefe parts, is not un- 
like a lurgeon's fyringe; let there alfo be made another cylin- 
der of brafs O P QK Fig. 5 of the magnitude of the figure, 
with two Alee or wings OS PS, and of liich a bore, as that 
its infide being made mto a female fcrew, it may be exafllf 
fitted to receive the male fcrew ; let the bore be enlar- 
ged from Rand Q^toTT; and let there be a /houlder 
V V : and make a plate W, perforated in the middle to fit the 
fhoulder, and be fixed thereto; make a right cone bored thro* 
its axis I z 5, Fig. 5; enlarge the bore from i 2, to 4 4; let 
there be a Ihoulder 5 5 to fit exaflly the cavity of the cylinder 
T T, and be firmly fixed therein ; let there be made a fpring 
Fig. 7, of brafs wire in a fpiral form round the cylinder, of 
a proper elafticity, and nearly equalling the diameter of the 
box 4 4 V V; but a little higher than the box, when left to 
itfelf, let it have at its lower extremity the plate 7 7 of the 
fame magnitude, whofe inferior part is to be armed with a 
fort leather moiftened in oil, to fhut the orifice of the fyringe ; 
then at the top of the cupping-glafs Fig. 8 , let there be a 
round bore, by which the cone is let down as far as the AldP 
SSj let the chinks or fiflures be filled with cement made of 
rofin, turpentine and lime, then let the lid 6 7 <J 7 Fig. 9, be wrap- 
ped up in leather ftecped in oil as high as the fhoulderby which 
the air, when exhaurted out of the glafs ( ftiould there hap- 
pen to be any fiflures in the little valve) may be excluded: 
When the thumb is applied clofe to the bore, the plate 9 9 
Fig. 10, is raifed by the handle to 10. 10; but becaufe at 
firfl the air only filled the fpace 909, it is now fo rarified, 
and expanded, as to take up the fpace 9 9. 10. 10. which is 
300 times greater than the former; wherefore the elafticity of 
the air included in the glafs, exceeding both the elafticities of 
the fpring, and of the air contained in the cylinder, the plate or 
valve will be thruft upwards, which will continue open, till 
fuch a quantity of air gets into the cylinder out of the glafs, as 
that the elafticity of the complement of air contained in the 
glafs fhall be equal to both the clafticities of the fpring 
and of the air now contained in the cylinder ; and 
upon opening the bore O, the valve J is ftrongly fhut by the 
preflure of the external air ; CdPteris paribus^ upon three or 
four fuflions, more or lefs, i ilH parts of air (according to the 
power of the fpring, and the ratio between the capacity of the 
cylinder and that of the cupping-glafs) will beexhaufled; and 
K k k 2 if 
