HYPOTHENUSE, in geometry, the long- 
est side of a right angled triangle ; or it is that 
side of which subtends the right angle. Eu- 
clid, lib. i. proposition 47, demonstrates, 
that, in every rectilinear right angled trian- 
gle, the square of the. hypothenuse is equal 
to the squares of both the other sides. This 
celebrated problem was discovered by Py- 
thagoras, who is said to have sacrificed a 
hecatomb to the Muses, in gratitude for the 
discovery. 
HYPOTHESIS, in general, denotes 
something supposed to be true, or taken 
for granted, in order to prove orillustrate 
a point in question. An hypothesis is 
either probable or improbable, according 
as it accounts rationally or not for any 
phenomenon; of the former kind we may 
reckon the Copernican system and Huy- 
gens’s hypothesis concerning the ring of 
Saturn ; and the Ptolemaic system may be 
esteemed an instance of the latter. 
HYPOXIS, in botany, a genus of the 
Hexandria Monogynia class and order. 
Natural order of Coronariae. Narcissi, 
Jussieu. Essential character : calyx a 
two valved glume ; corolla, six-parted, per- 
manent, superior ; capsule narrower at the 
base. There are fourteen species. 
HYRAX, in natural history, a genus of 
Mammalia, of the order Glires. Generic 
character: front teeth in the upper jaw 
two broad and somewhat distant; in the 
lower jaw four, broad, flat contiguous and 
notched ; grinders large, four on each side 
in both jaws; fore-feet, four-toed, hind-feet 
three-toed; no tail; no clavicles. What 
distinguishes this genus from the whole 
class of Glires, besides, is the circumstance 
of having four teeth instead of two in the 
lower jaw, and indeed, the teeth in general 
are differently formed. There are two 
species. 
H. capensis, or the Cape hyrax, is 
about as large as a rabbit, and abounds 
in the mountainous districts near the Cape 
of Good Hope, leaping from rock to rock 
with extreme agility, feeding by day, and 
retreating at night to the clefts and holes 
of the mountains. It has no power of 
burrowing any recess for itself. Its sound 
is a reiterated squeak. It subsists en- 
tirely on vegetable food, and prepares a 
bed for its repose and comfort in its fa- 
vourite recess. It may be easily fami- 
liarized, and in a state of domestication is 
extremely cleanly and alert. 
H. syriacus or the 'bristly hyrax, is to 
be met with particularly in Ethiopia and 
Abyssinia, and particularly under the rocks 
of the Mountains ( of the Sun. Its full 
length is about seventeen inches. These 
animals are called by the natives of these 
countiies Ashkokos. They are gregarious, 
and, occasionally, seen in companies of 
several scores basking before the clefts of 
the rocks in the open sunshine. They 
are gentle, weak and fearful, but if handled 
with roughness will bite with great severity. 
They are supposed to live on grain, fruits, 
and roots, and when kept in confinement, 
they will live upon bread and milk. They 
feed without any voracity, and even the 
pangs of hunger could not impel them to 
attack chickens or smaller birds which 
have been thrown to them in that state, 
in the way of experiment. Their motion 
is not firm upon their legs, but rather by 
stealing along, by a few paces at a time, 
upon their bellies, in the manner of the bat 
in approaching its prey. For the Hyrax, 
see Mammalia, Plate XII. fig. 5. 
HYPTIS, in botany, a genus of the Didy- 
namia Gymnospermia class and order. Na- 
tural order of Verticillate. Labiatas, Jus- 
sieu. Essential character : calyx turbi- 
nate ; corolla with a very spreading border ; 
lower lip semibifid ; anthers hanging down. 
There are two species. 
HYSSOPUS, in botany, hyssop, a genus 
of the Didynamia Gymnospermia class 
and order. Natural order of Verticillatae, 
Jussieu. Essential character : corolla, lower 
lip with a small middle crenate segment; 
stamens straight, distant. There are three 
species. 
HYSTERICS. See Medicine. 
HYSTRIX, porcupine, in natural history, 
a genus of 'quadrupeds of the order Glires. 
Generic character: two fore-teeth in the 
upper and the under jaw, cut obliquely ; 
eight grinders; body with spines and hair; 
toes four or five on the fore feet. There 
are five species. H. cristata, or the Com- 
mon porcupine, is about two feet in length, 
exclusively of the tail. It is found in Africa 
and India, and is seen not unfrequently in 
the warmer climates of Europe, particularly 
in Italy and Sicily. It is covered on the 
upper part of its body with variegated 
spines, or quills, which are long and sharp, 
and which, when irritated, it erects with 
particular intenseness, and a rustling and 
alarming noise, giving the idea of formidable 
hostility. It was supposed by the ancients 
to possess the power of darting these with 
unerring, and sometimes fatal, aim against 
its adversaries ; but it is ascertained to em- 
