xxiv DESCRIPTION OF PLATES. 



PLATE XXII. 



Fig. 288. Mr. Woltmann's hydrometrical fly. The plates A, B, are so adjusted 

 by experiment, as to move exactly or very nearly with the velocity of the wind, a few 

 degrees being allowed as a compensation for the retardation of friction. The cord C 

 is drawn up, and the wheel D is caused to revolve, at a time observed by a stop 

 watch ; and its surface is graduated so as to number the revolutions of the fly. 

 P. 243. 



Fig. 289. An apparatus for measuring a ship's way, resembling Captain Hamil- 

 ton's. A is a funnel partly covered, B a part of the ship's keel, C the upper part of 

 the pipe D, in which the smaller pipe E F slides in a collar of leathers, so as to have 

 the orifice F level with the surface of the water. This pipe has a small aperture at 

 the bottom, which limits the magnitude of the stream discharged into the vessel G, 

 the end F being considerably larger. The tube H serves as a gage, to measure the 

 velocity at any given time. P. 243. 



Fig. 290. An overshot wheel, on which the water is admitted in a retrograde 

 direction, so as to run off hi a continued stream ; at the lower part of the wheel it is 

 retained in the buckets partly by the assistance of a sweep. P. 245. 



Fig. 291. A breast wheel, with a sweep. P. 246. 



Fig. 292. An undershot wheel. P. 246. 



Fig. 293. A the form of the sail of a windmill : B the best inclination for each 

 part of the sail A, according to Smeaton's experiments. P. 247. 



Fig. 294. A kite supported by the wind, of which the force acts nearly in the line 

 A B, perpendicular to the surface of the kite ; and this, compounded with the force 

 of the cord A C, produces the result A D, which sustains the weight of the kite. 

 P. 247. 



Fig. 295. A ship working against a wind ; the force of the wind acting nearly in 

 the direction A B, perpendicular to the sails, the ship's real course is B C, the angle 

 C B D being the lee way. P. 249. 



Fig. 296. The anoria, or noria, used in Spain, for drawing water, by a series of 

 earthen pitchers, connected by ropes, and passing over a sprocket wheel. P. 250. 



Fig. 297. An undershot waterwheel, carrying fixed buckets, which raise a portion 

 of water, and deliver it into a trough, furnished with a projection, which stands 

 under the buckets, at the upper part of the wheel. P. 250. 



Fig. 298. A throwing wheel, for draining fens, worked by a windmill or other- 

 wise, and carrying the water upon a sweep from a lower to a higher level. P. 250. 



Fig. 299. The rope pump of Vera, for raising water by means of friction : the 

 rope is kept stretched by a pulley under the water, which is loaded with a weight, 

 and slides in a groove. P. 251. 



Fig. 300. The screw of Archimedes, nearly as described by Vitruvius. P. 251. 



Fig. 301. The screw of Archimedes, as recommended by D. Bernoulli. P. 251. 



Fig. 302. A waterscrew, revolving within a fixed cylinder. P. 252. 



Fig. 303. The spiral pump of Wirtz. P. 253. 



