DESCRIPTION OF PLATES. xxi 



PLATE XIX. 



Fig. 239. The surfaces of the fluid in the bent tube A B remain on the same 

 level, in the same manner as if the tube were absent, and the fluid made a part of 

 that which is contained in the reservoir CD. P. 197. 



Fig. 240. The bucket A being suspended by the rope B, and made to revolve 

 rapidly round its axis, the surface of the water assumes a parabolic form. P. 198. 



Fig. 241. A heavier fluid being contained in the upper part of the bent tube A B, 

 which is immersed in the lighter fluid, filling the vessel C D, the fluid in the tube 

 remains in a state of tottering equilibrium, when its surfaces are in the same level. 

 P. 198. 



Fig. 242. The fluid ABC presses on the bottom of the vessel B C with the same 

 force as if the vessel were of the form B C D E. P. 199. 



Fig. 243. The portion A B C D of the fluid being supposed to be congealed, and 

 then to form a part of the vessel, the pressure on the bottom would remain unaltered. 

 P. 199. 



Fig. 244. The weight A may be supported by the pressure of a small quan- 

 tity of fluid, either by making the surface of the vessel BC very large, and the 

 height of the tube D E moderate, or, while the vessel F remains of a moderate size, 

 by making the height of the tube G H very great. P. 199. 



Fig. 245. The pressure on any small part of the side of the vessel A B, at C or D 

 may be represented by the line C E, D F, and the whole pressure on the side by the 

 triangle B G, of which the centre of gravity is at H ; and if the side A I be sup- 

 ported by a single prop, it must be placed at the point K, the height of which is 

 equal to that of H. P. 200. 



Fig. 246. If the height of the surface A above B be to B C as the specific gravity 

 of the fluid in B C to that of the fluid in A B, the fluids will support each other. 

 P. 201. 



Fig. 247. Two square beams floating at the depths shown at A and B, will have 

 a certain degree of stability, but if they sink, as at C, they will overset. But a beam 

 of the breadth shown at D will always float securely. P. 202. 



Fig. 248. A jar containing images of fishes, with bubbles of air in them, which 

 sink when the cover of the jar is pressed with the hand. P. 202. 



Fig. 249. Dr. Hooke's semicylindrical counterpoise, by means of which a vessel 

 is kept always full. P. 203. 



Fig. 250. The form into which the flexible bottom of a cistern would be bent by 

 the pressure of the water ; the curve is the same as that into which an elastic rod 

 would be bent by forces acting at A and B. P. 203. 



Fig. 251. The bottle A, containing air and mercury, has the tube A B fitted into 

 it: and when the jar CD, in which it is enclosed, is exhausted by means of the air 

 pump, the elasticity of the air in the bottle forces the mercury up the tube. 

 P. 204. 



Fig. 252. An instrument for showing the buoyant effect of the air, called by 

 Boyle a statical baroscope ;* the index A shows, on the scale B C, the degree in 

 which the ball D is obliged to descend, by the diminution of the weight of the air. 

 P. 206. 



Fig. 253. The line denoting the natural density of the air, the line 1 A next 

 above it shows the degree in which the air is expanded at the height of a mile, and 1 B 

 the density of the air at the same height ; in the same manner IOC shows the expan- 

 sion of the air at the height of 10 miles, and 10 D its density ; and 5 E, below the line, 

 the density which it would acquire at the depth of 5 miles below the earth's surface. 

 The lines A C, D B E, are of the kind called logarithmic curves. P. 206. 



Fig. 254. The box or bason, in which the mercury of the common barometer is 

 contained : A is a float for adjusting the height, by means of the screw B, operating 

 on the leather which forms the bottom of the cavity. P. 209. 



* Ph. Tr. 1665, p. 231. 



