xxvi DESCRIPTION OF PLATES. 



PLATE XXIV. 



Fig. 324. The cupping instrument of Hero. The cavity A was partly exhausted 

 by applying the mouth repeatedly to the pipe B, the stopcock B being turned after 

 each application. When the stopcock C was opened, the air at D in contact with the 

 skin was also rarefied, and the effect of suction was produced. P. 260, 276. 



Fig. 325. Mr. Cuthbertson's air pump. When the piston rod A is depressed, it 

 leaves the piston B a little behind it, so as to make an opening between two conical 

 parts which are ground together, and the air escapes from the lower part of the barrel 

 into the upper part ; when it is elevated, the whole piston is raised, and a wire, which 

 slides through the axis of the rod, raises a small valve at the bottom of the barrel, 

 which leads to the receiver C, by the tube D E : the air is forced from the upper 

 part of the barrel through a valve in the oil vessel F, whence the oil runs back, when 

 it overflows, by a tube leading to the mouth of the barrel ; and if this tube be stopped 

 by turning its cock, the air may be condensed into a receiver fixed at G. At H is a 

 long gage, with a barometer immersed in the same bason of mercury. The piston rod, 

 which is hollow, has a perforation a little above A, to admit the oil, in order that the 

 wire may work freely in it. P. 261. 



Fig. 326. The two flies A and B being caused to revolve with equal velocities by 

 the descent of the weight C, they continue to move for an equal length of time in the 

 vacuum of the air pump. P. 261. 



Fig. 327. The air in the bottle A expands, when the receiver B is exhausted, and 

 causes the water to rise in a jet. P. 261. 



Fig. 328. A pear gage ; to be suspended in a receiver by a hook like that which 

 is shown in fig. 325. P. 262. 



Fig. 329. A condenser, with screws, for confining the receiver. A is a gage for 

 showing the degree of condensation ; B the piston of the syringe, with a valve of the 

 best kind, which is conical, and is confined by a spiral spring. But in common, 

 the valves are made of leather, with a plate of metal to strengthen it. P. 262. 



Fig. 330. A diving bell. A is the forcing pump, B a stopcock for letting out the 

 heated air, C a strong glass for giving light, D a float for the security of the diver. 

 P. 262. 



Fig. 331. Laurie's hydraulic bellows. When the vessel A is raised, the air enters 

 at the valve B ; when it is depressed, the valve B shuts, and the air is forced through 

 the pipe C D, which conducts it to the reservoir E, where it is confined by the valve 

 F, and forced by the pressure of the water through the pipe G. P. 263. 



Fig. 332. Mr. Watt's gasometer. The pressure is regulated by the magnitude 

 of the weights A and B, which act by the spiral fusees C, D, so as to sustain a part 

 of the weight of the inverted vessel, represented by the exterior dotted line. The gas 

 is admitted at E or F, and is delivered at G. G H is a gage for showing the height 

 of the water within and without the moveable vessel. I is a cock for letting off the 

 water. P. 263. 



Fig. 333. The shower bellows. The stream A, passing through the strainer B, 

 carries with it a quantity of air through the pipe C, which rises to the upper part of 

 the air vessel D, and is discharged by the pipe E. P. 263. 



Fig. 334. The centrifugal bellows. By the revolution of the fly, the air is caused 

 to enter at A, and is discharged at B. P. 264. 



Fig. 335. The original steam engine of Savery. The vessel A being filled with 

 steam from the boiler B, and the stopcock being turned, the steam cools and is con- 

 densed, and water is forced into its place by the pressure of the atmosphere, through 

 the valve C : the steam is then readmitted, and forces the water to ascend through 

 the valve D and the pipe D E. The vessel F acts alternately with A. P. 266. 



Fig. 336. The common steam engine of Newcomen and Beighton. The steam 

 being admitted into the cylinder A below the piston, the weight B is allowed to 

 descend : a jet of water is then admitted by the pipe C, which condenses the steam, 

 and the pressure of the atmosphere then depresses the piston : a part of this water is 

 admitted by the pipe D into the boiler, in order to keep it sufficiently full. P. 266. 



Fig. 337. Mr. Watt's steam engine. The steam, which is below the piston, is 

 suffered to escape into the condenser A by the cock B, which is opened by the rod 

 C, and at the same time the steam is admitted by the cock D into the upper part of 

 the cylinder ; when the piston has descended, the cocks E and F act in a similar 

 manner in letting out the steam from above and admitting it below the piston . The 



