PEK 
flieasuring distances upon tlie ground. Its 
external figure is shewn in figs. 1 and 2,' 
Plate Perambulator. A B is a mahogany 
wheel strongly framed and hooped with 
iron, that it may not wear, it turns in a 
handle, D E, which the operator holds in 
his hand, and thus wheels it along upon the 
ground. At F is a piece of mechanism 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, b, 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 B. 
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, 
h, 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, h, has a pi- 
nion on its arbor, immediately above it, 
turning k, which has pinion above it, turn- 
ing I, whose arbor is a tube, and put over 
the orb of h ; this tube has a short hand, 
m (fig. 5), fixed on it. The long hand, n, 
is fixed to the arbor of the wheel h j this 
arbor is not made fast to the wheel, but to 
a circular plate, p, against which the wheel 
tits,- 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, i, and thus give notice of the hand 
having completed its revolution. 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. The lower 
wheel on its arbor has thirty-six teeth, and 
^urns g, of twelve teeth, three times as 
fast, or once for four poles ; this is equal to 
one chain, and the circle of the hand, i, 
(fig. 5) which it carries, is divided into one 
hundred, each equal one link j the pinion 
PER 
dn the arbor of / has twelve teeth, and7r, 
which it turns, has forty, it will turn once 
for 3r times of /, or 3r times 12 poles = 40 
poles = 1 furlong, the dial of the hand, n, 
wliich it carries, is divided into forty, each 
equal one pole, and by the pin in the plate, 
p, it strikes the bell once each revolution. 
The pinion of eight on the arbor of /i, turns 
k, of sixty-four once for eight furlongs, and 
its pinion of six, drives I of seventy-two, 
once round for twelve of k, 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, without 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. 
PERGA, the perch, in natural history, a 
genus of fishes of the order Thoraeici. Ge- 
neric character : jaws unequal ; teeth sharp 
and incurvated ; gill-covers of three lami- 
na, 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 no- 
tice. 
P. fluviatilis, or the common perch, is 
generally from one to two feetlong, and two 
pounds and a half in weight, and inhabits 
the clear fresh waters of almost every coun- 
try in Europe, sometimes attaining the 
weight of ten pounds. It is gregarious, 
haunts those parts where the stream is gen- 
tle and profound, is extremely rapacious, 
catches with avidity at almost any bait, and 
tenacious of vitality to an extraordinary 
degree, surviving a journey of fifty miles, 
though packed up in dry straw. It. is 
highly valued both for its firmness and Ha- 
your, and among the Romans was held in 
very superior estimation. 
PERCEPTION, in logic, the first and 
most simple act of the mind, whereby it 
perceives or is conscious of its ideas. 
In bare perception, the mind is for the 
most part only passive; yet impressions 
made on the senses cause no perception, 
unless they are taken notice of by the mind, 
as we see in those who are intently busied 
in the contemplation of certain objects. 
It ought also to be observed, that the ideas 
