I 5 E R 
IP E fl 
3; 6 
PENTAPETES, a genus of the clode- 
randria order, in the monadelphia class of 
plants, and in the natural method ranking 
under the 37th order, columnifene. The 
■calyx is double; the stamina are 15 in num- 
ber, ot which five are castrated and long ; 
the capsule quinquelocular and polysper- 
rnous. There is but one species known in 
the gardens of this country, viz. the Phoe- 
nicia, with halbert-pointed, spear-shaped, 
^awed leaves. It is an annual plant, a na- 
tive of India. 
PENTHORUM, a genus of the penta- 
fynia order, in the pentandria class of plants. 
i he calyx is quinquefid ; there are either five 
petals or none; the capsule is five-pointed 
and quinquelocular. There is one species* 
PENTSLEMON, a genus of the didy- 
naniia angiospermia class and order. The 
calyx is live-leaved ; the corolla bilabiate, 
ventricose; rudiment of a 5th stamen, beard- 
ed above ; capsules two-celled. There are 
i2 speciesr 
PENUMBRA, in astronomy, a partial 
shade observed between the perfect shadow 
and the full light in an eclipse. 
It arises from the magnitude of the sun’s 
body; for were he only a luminous point, 
the shadow would be all perfect; but by rea- 
son of the diameter of the sun, it happens 
that a place which is not illuminated by the 
whole body of the sun, does yet receive rays 
from a part thereof. See Eclipse. 
PEP LIS, a genus of the monogynia order, 
in the hexandria class of plants, "and in the 
natural method ranking under the 17th order, 
cal\ canthemae. The perianthium is cam- 
panulated; the mouth cleft in 12 parts; 
there are six petals inserted into the calyx ; 
the capsule is bilocular. There are 2 species, 
creeping plants. 
PEPPER. See Piper. 
PERAMBULATOR, in surveying, an 
instrument for measuring distances, c-alled 
also pedometer, way-wiser, and surveying 
wheel. 
Plate Perambulator, &c. figs. 1, 2, and 3, 
represent a perambulator ; AA, fig. 1, is a 
wheel of mahogany, tired with iron, and 
made very strong; its circumference must 
be exactly ninety-nine inches, or half a pole. 
This is placed so as to turn round in an 
■opening cut in the piece BD, which forms 
the frame. In the arm B, a groove is cut 
from the centre of the wheel to the dial 
b\ the end of the spindle comes through 
the wood into this groove, and has' a small 
crown-wheel of eight teeth upon it. This 
works another wheel of eight teeth fixed on 
■a long spindle, which ■conveys motion from 
the w heel beneath to the dial b. The groove 
containing this spindle has a slip of wood 
screwed over it, to keep out dirt, &c. ; and 
the end of this spindle has a scpiare hole in 
it, into which is put the square end of the 
spindle a (fig. 2). 'Phis lias an endless 
screw d upon it, which works a worm-wheel e 
of twenty-four teeth, having a pinion of 
twelve beneath it : and below this has a wheel 
/of thirty-six. The pinion works the wheel 
g of forty ; and the wheel /turns the pinion 
A of twelve, whose spindle carries the short 
band of the dial (fig. 3). The arbour of the 
wheel g comes up. through the dial, and has 
the hand F fig. 3 on it ; as also a pinion of 
eight, which turns g of sixty-four. Tn the 
arbor of the wheel It, is a pinion i of six, tak- 
ing into k of seventy-two ; this is here sup- 
posed tojbe half broken away, to shew the 
wheels beneath. The spindle of this is hol- 
low, and is put over the arbor of the wheel 
g ; and carries the hand G fig. 3. IlliHH 
are four pillars, by which the two plates 
forming the frame for the wheels are held to- 
gether. The wheel g (fig. 2) is not fixed fast 
to its spindle, but is held between a brass 
plate / and another beneath ; the friction of 
these causes the wheel to turn the hand, and 
at the same time leaves the hand at liberty 
to be set without moving the wheels. The 
plate / has a pin n fixed in it ; which pin takes 
against a projecting part of the handle of the 
hammer in, so as to lift it up when the plate is 
turned, and let the spring p through re against 
the bell K. 
Wh en any distance is to be measured bv 
this machine, the operator takes hold of the 
handle, and wheels it along in as straight a 
line as he can. The circumference of the 
wheel being ninety-nine inches (or half a pole), 
and the two wheels in the piece being equal, 
the screw d (fig. 2) will turn once in each 
turn of the great wheel, or twice for every 
pole the machine is wheeled. This screw 
must be so cut that the great wheel must 
turn twenty-four times for one turn of the 
wheel e, and also the wheel / on the same 
spindle as this must turn a pinion h of one- 
third of its number of teeth, The short 
hand on the dial which it carries will for 
every revolution require eight turns of the 
great wheel, = four poles, = one chain. 
The circle is divided into 100 parts, each = 
one link. T he pinion of twelve on the arbor 
of the wheel e, turning once for twenty-four 
turns of the great wheel, makes the wheel g 
require for each revolution eighty turns of the 
great wheel, or for the machine to be wheeled 
ten chains {or turns of the short hand) = 40 , 
poles (as the circle of its hand is divided), i 
= one furlong : and at each revolution of this 
wheel, the hammer m will strike the bell K. 
The pinion of eight on the arbor of the wheel 
g, works h of sixty-four ; and its pinion i 
turns K of seventy -two; the result of which 
will be, that the hand on the spindle of k 
will require for each revolution 7080 turns of 
the great wheel, or for the machine to be 
wheeled 3840 poles, = 950 chains or turns 
of the short hand, = 96 furlongs or turns of 
the hand F and strokes on the bell, = twelve 
miles as the dial is divided. 
1 he use of this instrument is obvious from 
its construction. Its proper office is in the 
surveying of roads and large distances, where 
a great deal of expedition, and not much 
accuracy, is required. It is evident, that 
driving it along, and observing the hands, has 
the same effect as dragging the chain, and 
taking account of the chains and links. 
Its advantages are, its handiness and expe 
dition ; its contrivance is such, that it may 
lie fitted to the wheel of a coach, in which 
state it performs its office, and measures the 
road without any trouble. 
PERCA, Perch, a genus of fishes of the 
order thoracici ; the generic character is, 
teeth sharp, incurvate; gill-covers triphyl- 
lous, scaly, serrated ; dorsal fin spiny on the 
fore part ; scales (in most species) hard and 
rough. 
1 . Perea fiuviatilis, common perch. The 
PER 
1 perch is an inhabitant of clear rivers and 
Jakes throughout almost all parts of Europe, 
i arriving sometimes to a very large size, and 
to the weight of eight, nine, or ten pounds ; 
ils general size, however, is far smaller, usu- 
ally measuring from six to fifteen inches in 
length, and weighing from two ounces to 
four pounds. r Ihe colour of the perch is 
brownish-olive, sometimes accompanied bv 
a slight gilded tinge on the sides, and coin- 
monly marked by five or six moderately 
broad, blackish, transverse, semidecurrent 
bars ; the dorsal fin is of a pale violet-brown, 
marked at the back of the spiny part by a 
roundish black spot accompanied by a small- 
er one ; the rest of the fins, with the tail, are 
red. 
The perch usually spawns in the early part 
of the spring, depositing' a kind of extended 
bands of gluten, throughout which are- dis- 
posed the ova in a sort of reticular direction, 
it is of a gregarious disposition, and is fond of 
frequenting deep holes in rivers which flow 
with a gentle current; it is extremely vo- 
racious, and bites eagerly at a bait ; it is te- 
) nacious of life, and may be carried to the 
j distance of sixty miles in* dry straw, and yet 
survive the journey. It is one of those fishes 
which were held in repute at the tables of 
the antient Romans, and is in general esteem 
at the present day, being considered as firm 
and delicate. Iu some of the northern re- 
gions a species of isinglass is prepared from 
the skin. 
2. Perea lucioperca, sandre perch. Ge- 
neral length from one to two feet, but said 
sometimes to arrive at four feet ; shape long- 
er than in the preceding species, having some- 
thing of the habit of a pike, the head being 
rather produced, and the mouth furnished 
with large teeth: general colour silvery grey, 
deepest on the back, and with a pretty strong 
tinge of blue on the head and gill-covers ; 
1 sides of the back marked by prettv nfimer- 
’ ous, slightly decurrent, blackish bands ; 
j dorsal Jins, by numerous dusky spots ; pec- 
toral fins, reddish; the rest dusky. Native 
ot clear rivers and lakes in the middle parts 
i of Europe, and highly esteemed for the 
j table : in general manners said to resemble 
the common perch, but to be far less le- 
! nacious of life. 
[ 3. Perea cernua, ruffe perch. Length 
; about six inches; shape more slender than 
I that of the common perch; head rather large, 
1 and somewhat Hattened ; teeth small ; colour 
subolivaceous, with numerous dusky spots 
disposed over the body, dorsal, pectoral fins, 
and tail; abdomen whitish; native of many 
parts of Europe ; chiefly frequenting clear 
rivers, assembling in large shoals, and keep- 
ing in the deepest part of the water. There 
are about forty species of this genus. See 
Plate Nat. Ilist. figs. 323, 324. 
PERCH, in land-measuring, a rod or pole 
of 16$ feet in length, of which 40 in length 
and 4 in breadth make an acre of ground. 
But, by the customs of several counties, there 
is a difference in this measure. In Stafford- 
shire it is 24 feet; and in the forest of Sher- 
wood 25 feet, the foot being there 18 inches 
long ; and in Herefordshire a perch of ditch- 
ing is 21 feet, the perch of walling ]6£ feet, 
and a pole of denshiered ground is 12 feet, 
&c. 
PERCUSSION, in mechanics, the impre*- 
