r * r t , > s'- 
HYO 
Means of several placed at varied heights, 
the different degrees of moisture at differ- 
ent altitudes may be ascertained, &c. In 
fact, he considers the hygrometer, whether 
it is a prognostic of the weather or not, as 
a most valuable oracle to the farmer. See 
Weather. 
HYMEN, in anatomy, a membrane 
sometimes of a circular, sometimes of a 
semilunar figure, and sometimes of a form 
different from both. 
HYMEN/EA, in botany, a genus of the 
Decandria Monogynia class and order. Na- 
tural order of Lomentaceae. Leguminosae, 
Jussieu. Essential character: calyx five- 
parted ; petals five, almost equal ; style 
twisted inwards; legume filled with fari- 
naceous pulp. There is only one species, 
viz. H. courbaril, locust-tree. The wild 
bees are fond of building their nests in this 
tree, which grows to a considerable size in 
the West Indies, and is looked upon as ex- 
cellent timber; but it must be very old be- 
fore it is cut, otherwise the heart will be 
but small. It is in great request for wheel- 
work in the sugar-mills, particularly for cogs 
to the wheels, being remarkably hard and 
tough. Professor Jacquin says, that a cu- 
bic foot weighs about a hundred pounds, 
and that it yvill take a fine polish. 
HYMENOPTERA, in natural history, 
the fifth order of insects according to the 
Linnoean system. The insects of this order 
are furnished with four membranaceous 
wings, and also with a sting, or a process 
resembling one. The wasp and the bee are 
insects of this order. It consists of the fol- 
lowing genera : 
Ammophila 
Apis 
Chalcis 
Chrysis 
Cynips 
Formica 
Ichneumon 
Leucopsis 
Mutilla 
Scolia 
Sirex 
Sphex 
Tenthredo 
Thynnus 
Tiphia 
Vespa. 
HYOBANCHE, in botany, a genus of 
the Didynamia Angiospermia class and or- 
der. Natural order of Personate. p e di- 
culares, Jussieu. Essential character: ca- 
lyx seven-leaved ; corolla ringent, wilhout 
any lower lip ; capsule two-celled, many- 
seeded. There is but one species, viz. H. 
sanguinea, a native of the Cape of Good 
Hope, and is parasitical at the roots of 
shrubs. 
HYP 
HYOSCYAMUS, in botany, henbane , 
a genus of the Pentandria Monogynia class 
and order. Natural order of Luridae. So- 
laneas, Jussieu. Essential character: co- 
rolla funnel-form, obtuse ; stamina inclined ; 
capsule two-celled, covered with a lid. 
There are eight species. 
HY OSERIS, in botany, swine's lettuce or 
succory, a genus of the Syngenesia Polyga- 
mia iEqualis class and order. Natural or- 
der of Composite Semiflosculosi. Cicho- 
raceae, Jussieu. Essential character : calyx 
almost equal ; down hairy and calycled ; 
receptacle naked. There are ten species. 
HYPECOTJM, in botany, a genus of 
the Tetrandria Digynia class and order. 
Natural order of Corydales. Papaveraceas, 
Jussieu. Essential character : calyx two- 
leaved ; petals four, the two outer broader, 
and trifid ; fruit a silique. There are three 
species. 
HYPELATE, in botany, a genus of the 
Polygamia Monoecia class and order. Es- 
sential character: calyx five-leaved; co- 
rolla five-petalled ; stigma bent down, three- 
cornered ; drupe one-seeded. There is but 
one species, viz. H. trifoliata, a native of 
Jamaica, where it is common in the low 
lands. 
HYPERBOLA, in geometry, the sec- 
tion, GEH, (Plate VII. Miscel. fig. 5.) of 
a cone, ABC, made by a plane, so that 
the axis, E F, of the section inclines to the 
opposite leg of the cone, B C, which in 
the parabola is parallel to it, and in the el- 
lipsis intersects it. The axis of the hyper- 
bolical section will meet also with the op- 
posite side of the cone, when produced 
above the vertex, at D. 
Definitions. 1. If at the point E (fig. 6.) 
in any plane, the end of the rule EH be so 
fixed, that it may be freely carried round, 
as about a centre ; and at the other end of 
the rule H there is fixed the end of a thread 
shorter than the rule, and let the other end 
of the thread be fixed at the point F, in 
the same plane ; but the distance of the 
points E F must be greater than the excess 
of the rule above the length of the thread ; 
then let the thread be applied to the side of 
the rule E H, by the help of a pin G, and 
be stretched along it ; afterwards let the 
rule be carried round, and in the mean time 
let the thread kept stretched by the pin be 
constantly applied to the rule: a certain 
line will be described by the motion of the 
pin, which is called the hyperbola. But if 
the extremity of the same rule, which was 
Mm2 
1 9 
f 1 
1 
1 
■ 
■9H9MI 
HPPI 
