DESCRIPTION OF PLATES. xxvii 



jet is supplied by the water of the cistern G, which is pumped up at H from a reser- 

 voir : it is drawn out, together with the air that is extricated from it by the air pump 

 I, which throws it into the cistern K, whence the pump L raises it to the cistern M ; 

 and it enters the boiler through a valve, which opens whenever the float N descends 

 below its proper place. The pipes O and P serve also to ascertain the quantity of 

 water in the boiler. The piston rod is confined to a motion nearly rectilinear by the 

 frame Q ; the fly wheel R is turned by the sun and planet wheel S, T ; and the strap 

 U turns the centrifugal regulator W, which governs the supply of steam by the valve 

 or stopcock X. P. 267. 



Fig. 338. Mr. Symington's steam boat. A is the boiler, B the cylinder, C the 

 piston, D the condensation pipe, E the air pump, F stampers for breaking ice. 

 P. 267. 



Fig. 339. An air gun. The air is forced by the syringe A into the cavity sur- 

 rounding the barrel, whence it is discharged by the valve B, which is opened either 

 immediately by the action of the trigger C, or by a spring, which is bent by cocking 

 the gun, and set at liberty by the trigger. P. 269. 



PLATE XXV. 



Fig. 340. A series of waves or pulses of sound, diverging from one of the foci of 

 an ellipsis, and reflected towards the other. P. 293. 



Fig. 341. Waves diverging from a point near the centre of a circle, and converg- 

 ing after reflection to a point at an equal distance on the other side of the centre. 

 P. 293. 



Fig. 342. A section of a speaking trumpet and of a hearing trumpet : the lines 

 representing the direction of the sound before and after its reflections. P. 294. 



Fig. 343. A string impelled- by the bow of a violin, and lightly touched at the 

 same time at a point one third of its length from the end : the small pieces of paper 

 fly off from the middle of the vibrating portions, while the piece situated at the 

 remaining point of division retains its situation. P. 299. 



Fig. 344. A vibration compounded with another smaller vibration, three times 

 as frequent, in a transverse direction, the separate vibrations being such that the 

 points may be always opposite to a point moving uniformly in a circle. Thus the 

 vibrations in the lines A B and A C compose the complicated figure D E. P. 299. 



Fig. 345. A specimen of the manner in which the vibrations of a string are 

 usually performed when it is struck with a bow. P. 299. 



Fig. 346. Specimens of the simplest manner in which sand is collected into lines, 

 on a plate of glass or metal, which is made to sound by means of the bow of a 

 violin. P. 300. 



Fig. 347. A round plate, performing some of its most complicated vibrations, the 

 lines of division being indicated by the place of the sand. From Chladni. P. 300. 



Fig. 348. A square plate divided into a diversity of vibrating portions. From 

 Chladni. P. 300. 



Fig. 349. The small bones of the left ear, nearly three times the natural size, 

 supposed to be seen through the membrane of the tympanum, by looking directly 

 into the auditory canal. AB is the membrane of the tympanum, C the hammer, D 

 the anvil, E its attachment to the surrounding bone, F the stirrup, G the round 

 aperture in the bone leading to the cochlea. P. 302. 



Fig. 350. A view of the vestibule of the left ear, with the semicircular canals and 

 the cochlea, seen with the eye a little more depressed than by looking straight through 

 the canal, and exactly in the direction of the stirrup. AB C is the vestibule, imme- 

 diately behind the oval aperture, which is covered by the basis of the stirrup, D are 

 the canals, E the cochlea, the upper spire terminating in the vestibule, the lower in 

 the round aperture at B. The projection of the membrane of the tympanum is 

 marked by an oval line. P. 302. 



Fig. 351. The structure of the left ear, seen from above, the upper part of the 

 canal being supposed to be removed. A is the auditory canal, B the membrane of 

 the tympanum, C the hammer, D the anvil, E the stirrup ; Fthe place of the canals, 



