PET 
PET 
sential character : corolla one-petalled, fnn- 
nel fbrm ; stigma bifid ; berry many-seeded. 
There are three species. 
PETIOLUS. See Pehcnculus. 
PETIT (Peter) a considerable mathe- 
matician and philosopher of France, was 
born at Montlucon in the diocese of 
Bonrges in the year 1589, according to 
some, hut in 1600 according to others. He 
first cultivated the mathematics and philo- 
sophy in the place of his nativity ; but in 
1633 he repaired to Paris, to which place 
his reputation had procured him an invita- 
tion. Here he hecame highly celebrated 
for his ingenious writings, and for his con- 
nections with Pascal, Des Cartes, Mer- 
senne, and the other great men of that 
time. He was employed on several occa- 
sions by Cardinal Richelieu ; he was com- 
missioned by this minister to visit the sea- 
ports, with the title of the King’s Engineer; 
and was also sent into Italy upon the King’s 
business. He was at Tours in 1640, where 
he mari'ied ; and was afterwards made In- 
tendant of the Fortifications. Baillet, in his 
Life of Des Cartes, says that Petit had a 
great genius for mathematics ; that he ex- 
celled particularly in astronomy ; and had 
a singular passion for experimental philoso- 
phy. He was intiinately connected with 
Pascal, w ith whom he made, at Rouen, the 
same experiments concerning the vacuum, 
which Torricelli had befor e made in Italy ; 
and was assured of their truth by frequent 
repetitions. He died August the 20th, 1667, 
atLagny, near Par is, whither he had retired 
<br some time before his decease. He pub- 
lished several works upon physical and 
astronomical subjects, also on chronology 
and theology. 
PETITiA, in botany, so named in me- 
mory of Francis Petit, a genus of the Te- 
trandria Monogynia class and order. Na- 
tural order of Vitices, Jrtssieu. Essential 
character : calyx four-toothed, inferior ; 
corolla four-parted ; drupe with a two- 
celled nut. There is but one species, viz. 
P. Domingensis, a native of the island of St. 
Domingo. 
PETITION, no petition to the King, or 
to either house of parliament, for any alte. 
ration in church or state, shall be signed by 
above twenty persons, rrnless the matter 
thereof be approved by three Jrrstices of 
the Peace, or the major part of the Grarrd 
Jtrry in the county ; and in London, by 
the Lord Mayor, Aldermen, and Common 
Council : nor shall any petition be present- 
ed by more than ten persons at a time. 
Petition in chancery, a request in writ- 
ing, directed to the Lord Cliancellor, or 
Master of the Rolls, shewing some matter 
or cause whereupon the petitioner prays 
somewhat to be granted him. 
PETIVERIA, in botany, Guinea hen- 
weed, a genus of the Hexandria Tetragynia 
class and order. Natural order of Holora- 
cese. Atriplices, Jussieu. Essential cha- 
racter; calyx four-leaved; corolla none; 
seed one, with reflex awns at top. There 
are two species, viz. P. alliacea, common 
Guinea hen-weed ; and P. octandra, dwarf 
Guinea hen-weed : both natives of the 
W est Indies. 
PETREA, in botany, so named in honour 
of Lord Petre, a genus of the Didynaniia 
Angiospermia class and order. Natural 
order of Personata. Vitices, Jussieu. Es- 
sential character: calyx five-parted, veiy 
large, coloured ; corolla wheel-shaped ; cap- 
sule two-celled, at the bottom of the calyx ; 
seeds solitary. There is but one species, 
viz. P. volubilis, a native of South America 
and the West Indies. 
PETRIFACTION. See Oryctology. 
PETROCARYA, in botany, a genus of 
the. Heptandria Monogynia class and order. 
Natural order of Pomace®. Rosace®, 
Jussieu. Essential character; calyx tur- 
binate, five-cleft, with two bractes ' at the 
base; corolla five petalled, less than the 
calyx ; filaments fourteen, seven of which 
are barren ; drupe inclosing a two-celled 
nut, with a stony shell. There arc two 
species, viz. P. raontana, and P. campestris, 
both found in the woods of Guiana, where 
they grow to the height of forty and eighty 
feet. 
PETROLEUM, in chemistry. The sub- 
stances which mineralogists have distin- 
guished by the names of asphaltiim, maltha, 
petroleum, and naptha, are thought by Mr. 
Murray, and others, to be mere varieties of 
one species, and form a series which passes 
even into coal. Asphaltura foi-ms the con- 
nection with pitch-coal. It is found in 
veins, and in small masses, and also some- 
times on the surface of lakes. Maltha is 
softer, has a degree of tenacity, and a strong 
bituminous smell. Petroleum is semi-liquid, 
semi-transparent, of a reddish-brown colour, 
and fetid odour. Naptha is of a lighter co- 
lour, more or less transparent, perfectly thin 
and liquid, light, odoriferous, volatile, and 
inflammable. Naptha by inspissation be- 
coming petroleum, and this passing into 
asphaltum. See Asphaetem, Bitumen, 
&c. 
