PET 
in several parts of France petroleum is 
found floating on the water, and is known 
in commerce by the name of oil of Gabian. 
Wells jre sometimes dug 100 feet deep, 
where the petroleum is found mixed with 
tlie soil, in such proportion that ten pounds 
may be extracted from a iiundred weight. 
PETROMYZON, the lamprey, in natu- 
I'dl history, a genus of fishes of the order 
Cartilaginei. Generic character : body 
shaped like an eel ; mouth beneath, with 
numerous teeth, in circular rows ; seven 
spiracles on each side the neck ; no pecto- 
ral, or ventral fins. Shaw notices nine 
species, and Gmelin only four. P. marinus, 
or the great lamprey, is usually of a brown 
olive colour, tinged with yellowish-white. 
It is often three feet long ; is an inhabitant 
of the seas, as its name indeed implies ; but 
in the beginning of spring ascends rivers in 
which it resides for a few months, then 
returning to the ocean. It is viviparous, 
and supposed to subsist almost entirely on 
worms and fishes. Its heart is enclosed 
not in a soft, but in a cartilaginous pericar- 
dium, constituting thus a singular deviation 
from the general Structure of animals. Its 
spine also possesses the peculiarity of being 
rather a soft cartilage than bone. These 
fishes fasten themselves with the jagged 
edges of tlie mouth to large stones, with 
the most extraordinary firmness, and may 
be lifted by the tail to a considerable height 
without being made to (piit a stone of the 
weight of even ten or twelve pounds. Their 
principle of vitality is extremely vigorous 
and persevering, various parts of the body 
long continuing to move for some hours 
after it is divided ; and the head will 
adhere to a rock for hours after tire 
greater part of the body is cut away. In 
some large rivers of Europe these, fishes are 
taken in vast numbers, and preserved with 
spices and salt as an article for merchan- 
dise. In this country the Severn is the 
most celebrated river for them, and they 
are much valued on their fiist arrival from 
the sea. They are considered a high luxury 
for the table, and the life of one of the 
Kings of England will be recollected to 
have been terminated by his excessive par- 
tiality to potted lampreys. 
P. fluviatilis, or the lesser lamprey, is 
about twelve inches long, inhabits also the 
sea, but is found more fre(jufntly in the 
rivers than the former. It abounds in the 
Thames and Sevein, and is preferred by 
many to the larger species, as being not so 
strong in taste. In some years half a mil- 
VOL. V. 
PET 
lion of these fishes have been sold from the 
neighbourhood of Mortlake, for the Dutch 
cod and turbot fisheiy, at the rate of two 
pounds per thousand. In many parts of 
Germany they are fried and packed up in 
barrels with spices and bay leaves, and are 
conveyed to very distant regions, where 
tlrey are in high estimation, and sell for 
considerable pr ices. These fishes will live 
nrany days out of the water. In Russia 
they are taken from beneath the ice, pack- 
ed in snow and exported to great distances, 
and will generally recover themselves on be- 
ing afterwards thrown into the water. The 
planer lampi’ey is ten inches long, will live 
immersed in spirits of wine for fourteen 
minutes, moving during that tune with in- 
cessant violence. The leech lamprey is a 
native of the river Seine, and will fix on 
tire bellies of various fishes, particularly the 
shad, sucking their blood. 
PETTY, (Sir William), a singular in- 
stance of a universal genius, was the elder 
son of Anthony Petty, a clothier at Rum- 
sey in Hampshire, where be was born in 
the year 1623. While a boy he took great 
delight in spending his time among the 
artificers, whose trades he could work at 
when but 12 years of age. At the age of 
15 he was master of the Latin, Greek, and 
French languages, with arithmetic and those 
parts of practical geometry and astronomy 
useful in navigation. Soon after he went 
to the University of Caen in Normandy; 
and after some stay there he returned to 
England, where he was preferred in the 
King’s navy. In 1643, he went into the 
Netherlands and France for three years ; 
and having vigorously prosecuted his studies, 
especially in physic, at the Universities of 
Utrecht, Leyden, Amsterdam, and Paris, 
he returned home. In 1647, he obtained a 
patent to teach the art of double writing 
for seventeen years. In 1648, he published 
at London, “Advice to Mr. Samuel Hart- 
lib, for the advancement of some particular 
parts of learning.” At this time he adhered 
to the prevailing party of the nation ; and 
went to Oxford, where he taught anatomy 
and chemistry, and was created a Doctor 
of Physic, and grew into such repute that 
the philosophical meetings, which preceded 
and laid the foundation of the Royal 
Society, were first held at his house. In 
1650, he was made Professor of Anatomy 
there ; and soon after a member of the 
College of Physicians in London, as also 
Professor of Music at Gresham College, 
London. In 1652, he was appointed Pby- 
