PEN 
situJe of tlie figures desciibed by either of 
the points, will be in the same proportion to 
each other, as the distances of those points 
from the fulcrum, thus if the point / be 
the fulcrum, and if the distance from/ to 
g be half the distance from / to /t, the 
size of the figure desciibed by the point g 
will be half the size of the figure described 
at the same time by the point k. The ful- 
crum, as we have said before, can be chang- 
ed, as also the pencil and the tracer, and 
any of the three can be applied to either of 
the tubes upon the levers, if the tracer is 
placed in the tube li, the pencil ing, and the 
fidcrnra at/, any figure described by the 
tracer h, will be exactly copied one half the 
size by the pencil at g, and if on the contrary 
the pencil is placed at h, and the tracer at 
g, the figure drawn by the pencil will be 
twice the size of the original traced at g. 
When the fulcrum is placed between the 
two points at g, the figures rlescribed by 
each point will be inverted with respect to 
each other, though the same principle ap- 
plies, that the magnitude of the figures, 
will bear the same proportion to each other, 
as the distances of their tracing point from 
the fulcrum bear to each other. This last 
position of the instrument is seldom used 
on account of the figure being inverted, 
except when the figures traced and copied 
are equal to each other, or nearly so, as 
the first position will not allow of that. 
It will be easily seen that by the sliding 
motion of the tubes, g and /, the proportion 
between the three may be varied in any 
degree, and for this purpose the levers are 
engraved, and divisions made to set the 
tubes by, so as to reduce it in any propor- 
tion, and at the same time put the three 
points in the same right line,' otherwise the 
figures will be strangely distorted ; rannis 
a silk thread, which the operator hooks 
round bis fore finger, by pulling this he 
raises up the crayon, g, so that it will not 
mark ; each joint of the instrument is form- 
ed by a short axis, i, (fig. 2), made fast and 
moving with one lever, k, it has pivots at 
its ends, working in a small cock, I, screwed 
to the upper side of the other lever : be- 
neath each joint a small tube, »!, is screwed, 
its upper end receives the lower pivot of 
the axis i, and in the lower part a small 
spindle, n, is fitted, which has a castor at the 
bottom to support the weight of the instru- 
ment, by the turning of the spindle n the 
castor will run in any direction. One of 
these castors is also fixed at the outer end of 
the levers, A and B, as well as beneath each 
PEN 
Joint. Care should be taken that the table, 
upon which the instrument is used, is a per- 
fect plane, otherwise errors will arise from 
the tracer or crayon being sometimes thrown 
out of the perpendicular, and it is for the 
same reason that the levers are jointed 
with an axis as explained before. 
Fig. 4, Plate Pentagraph,is the common 
parallel ruler, A B are two rulers connect- 
ed by two bars CD, which are of equal 
lengths, and the distance between the pins 
by which the levers C D are fixed to the 
rulers, are the same distance from each 
other in both rulers, by this means it is 
easily seen, that the two rulers, A B, will al- 
ways move parallel to each other. 
Fig. 5, is another ruler differing from the 
other in being double ; the advantage of it 
over fig. 4, is, that the two rulers A B can 
be moved parallel to each other without 
sliding endways, as the other does, every 
part of the moving ruler describing the arc 
of a circle. 
PENTAMETER, in ancient poetry, a 
kind of verse consisting of five feet, or me- 
tres ; whence the name. The two first feet 
may be either dactyls or spondees, at plea- 
sure ; the third is always a spondee, and 
the two last anapests : such is tlie following 
verse of Ovid. 
1 2 3 4 5 
Carmini \ bus vi | ves tern | pus in o | mne meis. 
A pentameter verse, subjoined to an hex- 
ameter, constitutes what is called elegiac. 
PENTANDRTA, in botany, the name of 
the fifth class of plants in the Linnasan sys- 
tem, consisting of plants which have hei-ma- 
phrodite flowers with five stamina. There 
are six orders in this class, founded upon 
the number of styles. 
PENTAPETES, in botany, a genus of 
the Monadelphia Dodecandria class and or- 
der. Natural order of ColumniferEe. Mal- 
vaceje, Jussieu. Essential character: ca- 
lyx double, outer three-leaved ; inner five- 
parted ; stamina fifteen, with five ligules, 
petal-shaped ; capsule five-celled, many, 
seeded. There is but one species, ®iz. P. 
phcenicea, scarlet flowered pentapetes, a 
native of the East Indies and Japan. 
PENTHORUM, in botany, a genus of 
the Decandria Pentagynia class and order. 
Natural order of SucculentEe. Senipervi- 
vae, Jussieu. Essential character : calyx 
five or ten cleft ; petals none, or five ; cap- 
sule five-cusped, 'five-celled. There is only 
one species, viz, P. sedoides, American pen- 
thorura. 
