PTI 
ter : fractifications in an uninterrupted raar- 
frinal line ; involucre from the margin of the 
ftond turned in, uninterrupted, separating 
on the inner side. There are thirty- four 
species. 
PTEROCARPUS, in botany, a genus of 
the Diadelphia Decandria class and order. 
Natural order of Papilionaceae or Legnmi- 
nosuB. Essential character : calyx tive- 
toothed ; capsule sickle-shaped, leafy, vari- 
cose ; seeds few, solitary. There are six 
species, found chiefly in South America and 
the West Indies. 
PTERONIA, in botany, a genus of the 
Syngeriesia Polygamia jEqualis class and 
order. Natural order of Conipositae Dis- 
coidae. Cinarocephalse, Jussieu. Essential 
character : receptacle with many-parted 
bristles ; down subplumose ; calyx imbri- 
cate. There are eighteen species, all found 
at the Cape of Good Hope. 
PTEROSPERMUM, in botany, a ge- 
nus of the Monadelphia Dodeeandria class 
and order. Essential chai'acter : calyx sin- 
gle, five-parted ; corolla five-petalled : fila- 
ments fifteen, with five ligules, one between 
every three filaments; capsule five-celled, 
witli the cells two-valved ; seeds many, 
winged. There ime two species, viz. P. su- 
berifolium and P. acerifoliuin, both natives 
of the East Indies. 
PTEROTRACHEA, in natural history, 
a genus of the Vermes Mollusca class and 
order. Generic character : body detached, 
gelatinous, with a moveable fin at the ab- 
domen or tail ; two eyes placed within the 
head. There are four species. 
PTINUS, in natural history, a genus of 
insects of the order Coleoptera. Generic 
character; antennre filiform, the last joints 
larger ; thorax nearly round, not margined, 
receiving the head. There are about forty 
species, divided into sections : A. feelers 
clavate, lip entire. B. feelers filiform, lip 
bifid. Of the former section is P. pulsator, 
or death watch, which is of a dusky colour, 
with irregrdar grey brown spots. This in- 
sect is found in various parts of Europe in 
old wooden furniture, makes a peculiar 
ticking with the fore part of its head, re- , 
sembliiig the beating with the nail upon a 
table : this is done in several distinct 
strokes in the night time, and has been con- 
sidered by the common people as prophe- 
tic of some fatal occurrence in the family, 
but is nothing more than the call of one sex 
to the other. This must not be confounded 
with a much smaller insect of a very dif- 
ferent genus, which makes a sound like tlie 
PTO 
ticking of a watch, and continues for a long 
time without intermission. This belongs to 
a different order, and is the Termes pulsa- 
torium of Linnaeus. But the real death- 
watch of vulgar superstition is the ptinus. 
P. pertinax is brown, immaculate ; thorax 
compressed. It inhabits Europe, and is 
very destructive, to wooden furniture and 
books. When touched it draws in its head 
and legs, and becomes immoveable. 
PTOLEMAIC, or Ptolem.ean system 
of astronomy, is that invented by Claudius 
Ptolemy. This hypothesis supposes the 
earth immoveably fixed in tire centre, not 
of the world only, but also of the universe : 
and tliat the sun, the moon, the planets, 
and stars all move about it from east to 
west, once in twenty-four hours, in the or- 
der following, viz. the Moon next to the 
Earth, then Mercury, Venus, the Sun, Mars, 
Jupiter, Saturn, the fixed stars, the first 
and second crystalline heavens, and above 
all the fiction of their primum mobile. This 
system, or hypothesis, was first invented, 
and adhered to, chiefly because it seemed 
to correspond witli the sensible appearances 
of the celestial motions. 
PTOLEMY (Claudius), in biography, 
a very celebrated geographer, astronomer, 
and mathematician, among the ancients, 
was born at Pehisiura, in Egypt, about the 
seventieth year of the Christian era, and 
died, it has been said, in the seventy-eighth 
year of his age, and in the yeai- of Christ 
147. He taught astronomy at Alexandria, 
in Egypt, where he made many astronomi- 
cal observations, and composed his other 
works. It is certain that he flourished in 
the reigns of Marcus Antoninus and Adrian; 
for it is noted in his Canon, that Antoninus 
Pius, reigned twenty-three years, which 
shows that he himself survived him : he 
also tells us in one place, that he made a 
great many observations upon the fixed stars 
at Alexandria, in the second year of Anto- 
ninus Pius ; and in another, that he observed 
an eclipse of the moon in the ifinth year of 
Adrian ; from which it is reasonable to con- 
clude, that this astronomer’s observations 
upon the heavens were many of them made 
between the year 125 and 140. 
Ptolemy has always been reckoned the 
prince of astronomers among the ancients, 
and in his works has left us an entire body 
of that science. He has preserved and 
transmitted to us the observations and prin- 
cipal discoveries of the ancients, and at 
the same tiine augmented and enriched them 
with his own. He corrected Hipparchus’s 
