PEN 
pendulum, somewhat improved by Mr. 
Ci'ostliwaite, watcli and cloekmaker, Dub- 
lin, we have the following description, “ A 
and B (fig. 12), are two rods of steel forged 
out of the same bar, at the same time, of 
the same temper, and in every respect 
similari On the top of B is formed a gibbet 
C ; this rod is firmly supported by a steel 
bracket D, fixed on a large piece of marble 
E, firmly set into the wall F, and having 
liberty to move freely upwai'ds between 
cross staples of brass, 1, 2, 3, 4, which 
touch only in a point in front and rear (the 
staples having been carefully formed for 
that purpose) ; to the other rod is firmly 
fixed by its centre the lens G; of twenty- 
four pounds weight, although it should in 
strictness be a little below it. This pen- 
dulum is suspended by a short steel spring 
on the gibbet at C : all which is entirely 
independent of the clock. To the back of 
tlie clock-plate, I, are firmly screwed two 
cheeks nearly cycloidal at K, exactly in a 
line with the centre of the verge L. The 
maintaining power is applied by a cylindrical 
steel-stud, in the usual way of regulators 
at M. Now, it is very evident, that any ex- 
pansion or contraction that takes place in 
either of these exactly similar rods, is in- 
stantly counteracted by the other; whereas 
in all compensation pendulums composed of 
different materials, however just the calcula- 
tion may seem to be, that can never be the 
case, as not only different metals, but also 
different bars of the same metal, that are 
not manufactured at the same time, and 
exactly in the same manner, are found by 
a good pyrometer to differ materially in 
their degrees of expansion and contraction, 
a very small change affecting one and not 
the other.” The expansion or contraction 
of straight-grained fir-wood lengthwise, by 
change of temperature, is so small, that it 
is found to make very good pendulum rods. 
The wood called sapadillo is said to be still 
better. There is good reason to believe, 
that the previous baking, varnishing, gild- 
ing, or soaking of these woods in any melt- 
ed matter, only tends to impair the pro- 
perty that renders them valuable. They 
should be simply rubbed on the outside 
with wax and a cloth. In pendulums of 
this construction the error is greatly dimi- 
nished, but not taken away. 
PENGUIN. See Aptenobytes. 
PENELOPE, in natural histo-ry, a genus 
of birds of the order Gallina. By Latham, 
they are mostly arranged under the genus, 
Meleagris, or the Turkey. Their legs, how- 
PEN 
ever, are without spurs. They inhabit 
principally South America, and particularly 
Brasil and Guiana. The P. cristata, or guan, 
is two feet six inches in length. P. cu- 
manen.sis, or the yacon, is of the size of a 
hen turkey, and is found in Cayenne and 
Guiana. The Marail is found in flocks in 
Guiana, feeds on fruits, and roosts on trees. 
See Aves, Plate XL fig. 5. 
PENIS. See Anatomy. 
PENNANTIA in botany, so named in 
honour of Thomas Pennant, a genus of the 
Polygamia Dioecia, class and order. Es- 
sential character : calyx, none ; corolla five 
petalled; stamens five: pericarpium, three 
sided, two-celled, with solitary subtrique- 
trous seeds. There is but one species, viz. 
P. corymbosa, a native of New Zealand. 
PENNATULA, in natural history, sea- 
pen, a genus of the Vermes Zoophyta class 
and order; animal not affixed, of various 
shapes, supported by a bony part within, 
naked at the base, the upper part with ge- 
nerally lateral ramifications, famished with 
rows of tubular denticles producing radiate 
polypes from each tube. There are about 
eighteen species, of which P. coccinea is 
described as: stem round, radiating, with 
papillous polype-bearing sides, and clavate 
at the top. It is found in the White Sea, 
is soft, red, an inch and a half high, and. 
as thick as the little finger, wrinkled, with 
the papillae disposed in rows. P. phos- 
phorea has a fleshy stem, with a rough 
midrib, and imbricate ramification. It in- 
habits most seas, and emits a very strong 
phosphoric light in the dark ; about four 
inphes long, red, stem villous, with a lan- 
ceolate rough midrib, and nearly incum- 
bent rays, the tubes pointing all one way. 
P. reniformis ; stem round, vermicular, 
supporting a kidney-.shaped lehf-like head, 
pi'oducing polypes on one surface. It in- 
habits South Carolina : body expanded, 
kidney-shaped, flat, rising from a short 
round stem, and covered on the upper sur- 
face with numerous tubular orifices, through 
which the polypes are obtruded at pleasure ; 
the upper surface is of a rich purple, the 
under side brilliant, and sometimes yel- 
lowish. 
PENNY, an ancient silver coin, which, 
though now little used, was the only one 
current among our Saxon ancestors. It 
was then equal to j^th part of a pound. 
In Etheldred’s time the penny was the 20th 
part of the Troy ounce, hence the denomina- 
tion penny-weight. Till the time of Edward 
the first, the penny was struck with a cross 
