PEN 
PEN 
PEN 
from left to right. The fleshy filaments, or 
claws, move in all direct. ons; and witn the 
cylindrical part from which they proceed are 
sometimes protruded from the tins, and some- ■ 
times hidden with them. 
Upon dissecting this animal the following 
phenomena were discovered: When the 
trunk was opened lengthwise, a saltish liquor 
flowed out of it, so viscid as to hang down 
an inch. The whole trunk of the stem was 
found to be hollow, the outward membrane 
being very strong, and about the tenth part 
of an inch thick ; within this membrane ap- 
peared another much thinner; and between 
these two membranes, in the pinnated part 
of the trunk, innumerable liitle yellowish 
eggs, about the size of a white poppy-seed, 
were seen floating in a whitish liquor; about 
three parts of the cavity within the inner 
membrane is tilled by a kind of yellowish 
bone; this bone is about two inches and a 
half long, and one twentieth of an inch thick; 
in the middle it is square, but towards 
the ends it grows round and very taper, that 
end being finest which is next the pinnated 
part of the trunk. This bone is covered in 
its whole length with a clear yellowish skin, 
which at each end runs out into a ligament ; 
one is inserted in the top of the pinnated 
trunk, and the other in the top of the naked 
trunk; by the help of the upper figament the 
end of the bone is either bent into an arch, 
or disposed in a straight line. I he tins are 
composed of two skins ; the outward one is 
strong and leathery, and covered over with 
an infinite number ot crimson streaks ; the 
inner skin is thin and transparent; the suck- 
ers are also in the same manner composed ot 
two skins, but the outward skin is something 
softer. Both the fins and suckers are hollow, 
so that the cavity of the suckers may com- 
municate with those of the fins, as the cavity 
of the fins does with that of the trunk. Dr. 
Shaw, in the History of Algiers, says, that 
these animals are so luminous in the water, 
that in the night the fishermen discover fishes 
swimming about in various depths of the 
sea by the light they give. From this extra- 
ordinary quality, Linnaeus calls this species of 
the sea-pen pennatula phosphorea ; and re- 
marks, after giving the synonyms of other 
authors, habitat in oceano funduin illumi- 
nans. 
There are other kinds of sea-pens, or spe- 
cies of this animal, which have not a resem- 
blance to a pen. 
PENNY, formerly a silver, but now a 
copper coin. 
The penny was the first silver coin struck in 
England by our Saxon ancestors, being the 
240th part of their pound, and its true weight 
was about 22i grains troy. 
In Etheldred’s time, the penny was the 
20th part of the troy ounce, and equal in 
weight to our threepence; which value it 
retained till the time of Edward the Third. 
Till the time of king Edward the First, the 
penny was struck with a cross so deeply sunk 
in it, that it might, on occasion, be easily 
broken, and parted into two halves, thence 
called halfpence; or into four, thence called 
fourthings, or farthings. But that prince 
coined it w ithout the cross; instead of which 
he struck round halfpence and farthings : 
though there are said to be instances of such 
round halfpence having been made in the 
reign of Henry the First, if not also in those 
o the two Vv iliiams. 
Edward the First also reduced the weight 
>of the penny to a standard ; ordering that it 
should weigh 32 grains of wheat, taken out 
of the middle of the ear. This penny was 
called the penny sterling; and 20 of them 
were to weigh an ounce, whence the penny 
became a weight as well as a coin. 
By the 9th of Edward, the Third, it was 
diminished to the 20th part of the troy 
ounce; by the 2d of Henry the Sixth it was 
the 32nd part ; by the 5th of Edward the 
Fourth, it became the 40th, and also by the 
36th of Henry the Eighth, and afterwards 
the 45th; but by the 2nd of Elizabeth, 00 
pence were coined out of the ounce, and 
during her reign 02, which last proportion is 
still observed in our times. 
Penny-weight, a troy weight, being 
the 20th part of an ounce, containing 24 
grains ; each grain weighing a grain of w heat 
gathered out of the middle of the ear, well 
dried. The name took its rise from its being 
actually tire weight of one of our ancient 
silver pennies. See Penny. 
PENTAGON, in geometry, a figure of 
five sides and five angles. 
If the five sides are equal, the angles are 
so ton, and the figure is called a regular pen- 
tagon; such is ABODE (Plate Miscel. tig. 
'184), inscribed in the circle. 
The most considerable property of a pen- 
tagon is, that one of its sides DE,' is equal in 
power to the sides of a hexagon and a de- 
cagon, inscribed in the same circle ABODE; 
that is, the square oflthe side DE, is equal to 
the sum of the squares of the sides ^E and 
'E5. 
The area of a pentagon, like that of any 
other polygon, may Ire obtained by resolv- 
ing it into triangles. See the articles Tri- 
angle and Polygon. 
Pappus lias also demonstrated, that twelve 
regular pentagons contain more than twenty 
triangles inscribed in the same circle. 
The dodecahedron, which is the fourth 
regular solid, consists of twelve pentagons. 
In fortification, pentagon denotes a fort 
with five bastions. 
PENT AG R A P H , or Parallelogram, 
an instrument whereby designs of any kind 
may be copied in w bat proportion you please, 
without being skilled in drawing. 
A pentagraph is composed of 4 bars, 
ABDE, Plate Pedometer, &c. fig. 4, usually of 
brass ; the bar A is jointed to B at b about lie 
middle, and at a it is connected with E: the 
bar B is the same length as A ; and at d is 
jointed to the bar D, whose end is connected 
with the end of E; these four bars forma 
parallelogram : thus, ha = D, and bd — E. 
To the other end of the bar A, a tube F is 
soldered, through which a pointed brass rode, 
called the tracer, is put ; the end of the bar 
B lias a slider G upon it, which lias a tube 
similar to F ; another slider I of the same 
kind is mounted on the bar D. These sliders 
have screws, by which they can be fixed at 
any distance. Under each of the joints of 
the base, a small tube is fixed, in the bottom 
of which is a small castor as H, which makes 
the instrument run easily on the table. When 
the instrument is used, the two sliders G l 
must be set exactly in a line with the tube 
F ; when it is required to make a copy of a 
drawing of the same size, the sliders must 
375 
be set so that from F to I is the same dis- 
tance as from I to G; the tube 1 must then 
have a wire put through it, whose lowest end 
is fast screwed to a heavy leaden weight, L ; 
this must have three sharp points in the 
under side, so that when it is set on the table 
it may not be liable to move; then it a de ign 
or drawing is laid under the tube F, and 
the point of the tracer drawn over the lines 
of it, the point of the pencil at G will de- 
scribe a similar figure. If the drawing is to 
be reduced to one-half of the size, the w eight 
must be put to the slider G, and the pencil 
into I, without moving either slider ; then 
the distance from the tracer to the fixed 
point or weight L, is twice the distance of the 
pencil to the weight. The rule fur setting 
the sliders for any proportion is, as the dis- 
tance between the tracer t and the fixed 
point L, is to the distance between the pencil 
G and the s me, so is tire length ot ; 11 y line 
described by the tracer, to the length of the 
hne at the same time described by r thq 
pencil. To avoid the trouble of measuring 
these distances each time, the bars B and D 
are divided into ten or twenty of the most 
common proportions, by which divisions the 
sliders are to be fixed. 
The construction of one of the sliders is 
shewn in fig. 5: where M is a piece of brass, 
to one corner of which a tube g is soldered; 
an opening of the same width as the bar is 
cut in this, and a cover N is screwed on with 
two screws: this cover has a screw with a 
mill-head through it, by which the slider is 
fixed. Apiece of brass O, a little bent, is put 
between the bar and the under s de of the 
cover, and whose elasticity prevents the 
slider moving too freely when the screw is 
slack, and defends the bar from being scratch- 
ed by the ends of the screw when it is fixed. 
Fig. 0, describes the method of making 
the joints of the rods : P is the end of one 
bar, which has a steel spindle p shewed fast 
to it ; the other bar n has a cock v, screwed 
on, whose upper end projects over the tube 
t, and has a hole through it, just over the hole 
in the tube. The ends of the spindle P are 
put “between the Iroles in the cock and the 
hole in the tube ; if the spindles are well 
fitted, this joint is very steady, and without 
any shake. The lower end of the tube t has 
a hole drilled in it, into which the spindle W 
of the castor is put ; the castor is kept from 
falling out of the tube, by the point ot a small 
screw going through the side of the tube t, 
which takes into a notch cut round in the 
top of the spindle w. When the machine is 
used, a fine line, RE, is put through rings in 
the cocks bd, and tied to the pencil ; the 
other end has a loop to be hooked over the' 
thumb of the operator, by pulling w hich he 
can raise the pencil at D, when lie does not 
wish it to mark. 
PENTAMETER, in antient poetry,, a 
kind of verse consisting of five feet, or metres, 
whence the name. 
PENTANDRIA, in botany, one of Lin* 
nasus’s class of plants, the fifth in order ; tire 
characters of which are, that all the plants 
comprehended in it have hermaphrodite 
flowers, with five stamina or male parts in- 
each; they are subdivided into orders, which 
are denominated monogynia, digynia, tri- 
gynia, &c. according as there are one, two,, 
tiiree, &c. pistils, or female parts, in each 
flower. 
