PER 



PER 



laid on a plate of clear glass ; and if ap- 

 plied first to the third magnifier, then to 

 the second, and finally to the first, will 

 show tin different animalcules it contains, 

 of several kinds a d shapes, as well as 

 sizes. 



PEPPERMINT, a species of mint. See 

 MENTHA. 



PERAMBULATOR, a machine for 

 measuring 1 distances upon the ground. 

 Ls external figure is shewn in figs. 1 and 

 2, Plate Perambulator. A B is a maiio- 

 gatiy wheel, strongly framed and hooped 

 \vith iron, that itma^ not wear, it turns in 

 a hanaie, D E, which the ope i at or holds 

 in his hand, and thus wheels it along upon 

 the ground. At F is a piece of mechan- 

 ism to register the number of revolutions 

 the wheel has made. The pivots of the 

 wheel work into pieces of brass let into 

 the two arms of the handle, D E ; on the 

 end of one of its pivots, a small pinion, a, 

 (fig. 3) is fixed, this turns another pinion, 

 *, upon a long spindle, d, which conveys 

 the motion to the machinery at F (fig 2) ; 

 both pinions have eight teeth, therefore 

 the spindle, d, turns in the same time as 

 the great wheel, A JJ. This spindle is 

 let into the wood work of the handle, as 

 is shewn in the dotted line, d, (fig. 2), and 

 has a square hole in its end to receive the 

 end of a short arbor, e, (fig. 4), which is 

 an enlarged plan of the wheel work; this 

 end has an endless screw on it turning a 

 wheel, /; below this wheel, on the same 

 arbor, is a pinion turning a wheel, A, and 

 lower still is another wheel (hidden by /), 

 turning a pinion, g, on whose arbor is the 

 small hand, i, shewn in the plan of the 

 dial plate. The wheel, A, has a pinion on 

 its arbor, immediately above it, turning k, 

 which has a pinion above it, turning/, whose 

 arbor is a tube, and put over the orb of h ; 

 this tube has a short hand, m (fig. 5), fix- 

 ed on it. The long hand, w, is fixed to 

 the arbor of the wheel h ; this arbor is 

 not made fast to the wheel, but to a circu- 

 lar plate,/*, against which the wheel fits, 

 and to which it is held by a pin put 

 through the arbor beneath it, by this 

 means the hands can be turned round to 

 set them, without moving the wheel h ; a 

 pin is fixed in this wheel, which a, every 

 revolution, lifts and lets fall a hammer, r, 

 to strike the bell, /, and thus give notice 

 of the hand having completed its revolu- 

 tion. The great wheel is half a pole in 

 circumference, and the wheels a b, being 

 equal, the endless screw turns once for 

 every half pole the instrument is wheeled 

 along the ground ; the screw is so cut, 

 that it turns the wheel,/, once in twenty- 



four turns of the great wheel equal twelve 

 poles. Thf lower wheel on its arbor has 

 thirty- s,x teeth, and turns g t of twelve 

 teeth, ihree times as last, or once for four 

 poles; this is equal to one chain, and the 

 circle of >.he hand, z, (fig. 5) which it car- 

 ries, i?, divided into one hundred, each 

 equal one link ; the pinion on the arbor of 

 /lias twelve teeth, and A, which it turns, 

 has forty, it will turn once for 3^ rimes of 

 /, or 3 j times 12 poles = 40 poles = 1 

 furlong, the dial of the hand, n, which it 

 carries, is divided into forty, each equal 

 one pole, and by the pin in the pjate, p, it 

 strikes the bell once each revolution. The 

 pinion of eight on the arbor of A, turns k, 

 of sixty-four once for eight furlongs, and 

 its pinion of six, drives / of seventy -tvx>, 

 once round for twelve of A 1 , or ninety-six 

 furlongs, equal twelve miles. The hand, 

 m, fixed to its arbor, points out these dis- 

 tances on a circle divided into twelve for 

 miles, and subdivided into eight for fur- 

 longs. A. small scraper is fixed to the 

 frame to prevent the wheel gathering dirt, 

 and thus enlarging its circumference. 



In wheeling a machine along a road, 

 care should be taken to avoid all sudden 

 holes or hills as much as possible, with- 

 out deviating from the straight line. 



The bell, by striking, is of great use to 

 point out every furlong which might other- 

 wise be passed unnoticed. 



PERCA, the />ercA, in natural history, a 

 genus of fishes of the order Thoracici. 

 Generic character : jaws unequal ; teeth 

 sharp and incurvated ; gill-covers of three 

 lamina, scaly and serrated; dorsal fin 

 spiny on the fore part ; scales generally 

 hard and rough. There are sixty species, 

 of which the following is most deserving 

 of notice. . 



P. fluviatilis, or the common perch of 

 England, is generally from one to two 

 feet long, and two pounds and a half in 

 weight, and inhabits the clear fresh wa- 

 ters of almost every country in Europe, 

 sometimes attaining the weight of ten 

 pounds. It is gregarious, haunts those 

 parts where the stream is gentle and pro- 

 found, is extremely rapacious, catches 

 with avidity at almost any bait, and tena- 

 cious of vitality to an extraordinary degree, 

 surviving a journey of ftfty miles, though 

 packed up in dry straw. It is highly va- 

 lued both for its firmness and flavour, and 

 among the Romans was held in very su- 

 perior estimation. 



P. striatus. Pale brown or whitish, with 

 about eight lines running parallel .with 

 each other, on the sides. This is the fish 



