778 



PLATE XXI. 



Fig. 2(53. A stream of air being forced through the 

 pipes A tind B, the mercury in the barometer C D 

 Calls from C to D. P. 29r. 

 - Vig. *ti9. A stream entering the reservoir A, by the 

 pipe B,carrics with it all the vvaterC,vvhich stands above 

 the level of its upper surface. P. 297. 



Fig. 270. The ball A is permanently supported by 

 tJie jet B, because, when it fulls into the position here 

 represented, the centrifugal force of the water at A 

 cairics it back to the middle of the jet. P. 208. 



Fig. 271. A plate, bent into the form A BC, turn- 

 in:; on the centre B, is impelled by a stream of air 

 D in the direction C D. I'. 298. 

 - Fig. 272. A cylinder moveable on an axis, with two 

 curved pipes inserted in its lower part, seen from 

 above. The stream A enters at the top of the cy- 

 linder, and is discharged by the orifices B, C, so as to 

 turn the vessel in the direction B D. P. 301. 



Fig. V3. A jet of a Huid, striking on an obstacle 

 of equal diameter, and separated by it so as to con- 

 tinue its motion obliquely. P. 302. 



Fig. 274. The whole resistance directly opposed 

 to tlie sutfacc A'B being represented by BC, the por- 

 tion which, according to Uie principles of the reso- 

 lution of forces, ought to at t on the wedge A B U, is re- 

 presented by B E; and in the same manner the resist- 

 ance on AB F is to the whoje as B G to BC. P. 303. 



Fig. 275. The form of the dead water moving before 

 an obtuse body is nearly like that of ABC; and the 

 form adiiptcd for moving through the water with the 

 least possible resistance like A BDC. P. 804. 



Fig. 276. The direction in wliirh the particles of a 

 fluid arc supposed to move when they strike against a 

 concave surface. P. 305. 



Fig. 277. A hydrostatic balance. P. 309. 



Fig. 278. Mr. Nicholson's hydrometer, to be em- 

 ployed with weights, for finding the specific gravity of 

 Muids or solids. P. 309. 



Fig. 279. A spirit level. P. 311. 



Fig. 20O. An overflowing lamp. The hemispheri- 



cal counterpoise, wliich is so loaded, that its centre of 

 gravity is at A, raises the surface of the heavy fluid B 

 tlte higher as it is more exhausted, so that the oil C 

 is always forced up nearly to the level of the wick at D. 

 The oil is poured in by a pipe, in the middle of the 

 cylindrical column. The air holes may bo made 

 wherever it is most convenient. P. 311. 



Fig. 281. A section of an embankment, of a proper 

 form to be opposed to the sea, with a drain passing 

 through it, and a valre at its opening. P. 312. 



Fig. 282. The form recommended for the section 

 of a river or canal. P. 313. 



Fij. 283. A B shows the strongest form for a'vertical 

 beam, fixed above and below, and calculated to resist 

 the pressure of a'fluid; the greatest thickness being at 

 C ; and D E is the outline of a series of horizontal 

 planks, of such a thickness as to afford equal strength 

 throughout the sluice or floodgate. P. 314. 



F'ig. 281. A box, with a valve supported by a hol- 

 low ball, for letting out air from pipes, when it is be- 

 low the level of the reservoir. P. 310. 



Fig. 285. Two methods of letting out air from pipes, 

 when it is above the level of the reservoir; A a valve 

 with a stopcock near it; B a vessel of water, screwed 

 on for receiving the air ; to be replenished with water 

 as it becomes empty. P. 317. 



Fig. 286. A section of a compound stopcock, which 

 receives a fluid from either of the pipes A, B, or C, 

 into a cavity which descends a little in the direction 

 of the axis, and communicates with the pipe D, by 

 riicans of one of thfe 'bores represented by dotted lines, 

 according to the position into which the moveable cy- 

 linder is turned. P. 318. 



Fig. 287. Valves of difterent kinds; A the commoA 

 clack valve; B a double clack valve, consisting of two 

 semicircular valves; C a pyramidical valve, consisting 

 of four triangular pieces; U a circular valve turning on 

 an axis; E, a stcain valve of metal, sometimes called 

 a T valve, F, a valve of oiled silk or bladder, support- 

 ed by a grating, for air. P. 318. 



