HEA

HEADBORROW, or HEADBOROUGH, the chief of the frank pledge, and he that had the principal government of them within his own pledge. He was called also burrowhead, bursholder, third-burrow, tithing-man, chief-pledge, or borrow-elder. He is now occasionally called a constable.

HEALTH, is a right disposition of the body, and of all its parts; consisting in a due temperature, a right conformation, just connection, and ready and free exercise of the several vital functions.

HEARING. See SOUND.

The organ of hearing is the ear, and particularly the auditory nerve and membrane. See ANATOMY and PHYSIOLOGY.

HEAT. The laws according to which the temperature of bodies is subject to increase or diminution, have been discussed in the articles CALORIC, CAPACITY, COLD, COMBUSTION, and CHEMISTRY. In the first of these articles, caloric was considered as a substance capable of passing from body to body, and subsisting in them in different states. This is the general doctrine of chemical philosophers: many of these, however, as well as others, incline to the hypothesis, that heat may consist in an undulatory or other intestine motion, either in the parts of bodies, or in some subtle fluid, or ETHER, which see. Among these, we may reckon Sir Isaac Newton, Mr. Cavendish, Dr. Young, and Count Rumford.

“If heat,” says Dr. Young, “when attached to any substance, be supposed to consist in minute vibrations, and, when propagated from one body to another, to depend on the undulations of a medium highly elastic, its effects must strongly resemble those of sound, since every sounding body is in a state of vibration; and the air, or any other medium, which transmits sound, conveys its undulation to distant parts, by means of its elasticity: and we shall find, that the principal phenomena of heat may actually be illustrated by a comparison with those of sound. The excitation of heat and sound are not only similar, but often identical; as in the operations of friction and percussion: they are both communicated sometimes by contact, and sometimes by radiation; for, besides the common radiation of sound through the air, its effects are communicated by contact, when the end of a tuningfork is placed on a table, or on the sounding-board of an instrument, which receives from the fork an impression that is afterwards propagated as a distinct sound. And the effect of radiant heat, in raising the

temperature of a body, upon which it falls,
resembles the sympathetic agitation of a
string, when the sound of another string,
which is in unison with it, is transmitted to
it through the air. The water, which is
dashed about by the vibrating extremities
of a tuning-fork dipped into it, may repre
sent the manner in which the particles at
the surface of a liquid are thrown out of the
reach of the force of cohesion, and con-
verted into vapour; and the extrication of
heat, in consequence of condensation,
may be compared with the increase of
sound produced by lightly touching a chord
which is slowly vibrating, or revolving in
such a manner as to emit little or no audi-
ble sound; while the diminution of heat by
expansion, and the increase of the capacity
of a substance for heat, may be attributed
to the greater space afforded to each parti-
cle, allowing it to be equally agitated with
a less perceptible effect on the neighbour-
ing particles. In some cases, indeed, heat
and sound not only resemble each other in
their operations, but produce precisely the
same effects; thus, an artificial magnet,
the force of which is quickly destroyed by
heat, is affected more slowly in a similar
manner, when made to ring for a consider-
able time; and an electrical jar may be dis-
charged, either by heating it, or by causing
it to sound by the friction of the finger."
See the articles first mentioned.

HEAT, animal. The temperature which animals, and even vegetables maintain during life, above that of surrounding ob jects, is a very striking phenomenon. By general analogies it has frequently been re. ferred to the process of combustion; and from facts more distinctly pointed, the doc trine, that it depends upon the absorption of oxygen, has been advanced by modern chemists. But it is to Dr. Crawford we are indebted for a direct series of experiments, by which the nature of the process is directly made out. It would carry us too far into physiological disquisition, if we were to proceed to enquire respecting the nature of the parts, and the functions of organized beings. The blood which circulates through the lungs absorbs oxygen in the act of respira tion, by means of which a portion of the carbon which it contains is acidified and carried off in the elastic state. After this, and perhaps other changes, the fluid passes through the arteries to the extreme vessels, depositing in some manner the elementary parts or principles of animal matter during the act of nutrition, in which state of still

HED

further change the blood returns by the
veins, and again passes through the course
of circulation. From his experiments on
the capacities of arterial and venous blood,
Dr. Crawford found the capacity of the
former for heat to be 1.030, and that of the
latter only 0.892, whence he concludes, that
though heat must be given out in conse-
quence of the diminished capacity of the
combined oxygen absorbed by respiration,
yet the increased capacity of the arterial
blood will prevent its becoming sensible
immediately in the lungs; instead of which,
it will be given out at the smaller ramifica-
tions where the blood becomes changed in
its nature, and in its capacity for heat by
its conversion to the venous state. It has
also been established by the experiments of
the same philosopher, that the process of
absorption of oxygen is less in a higher than
in a low temperature; the difference be-
tween the arterial and venous blood being
at the same time less, and consequently the
augmentation of temperature in the animal
less considerable. This law of the animal
economy, assisted by the increased evapo-
ration, and by the slow conducting power
of an animal body, and perhaps by the per-
manency of the enlarged capacity, seems
sufficient to account for the power which
animals possess of maintaining their na-
tural temperature without any remarkable
change in an atmosphere greatly heated,
as was shewn in the experiments of For-
dyce and Blagden. (See Philos. Trans.
1775.) It must be confessed, however,
that some farther investigations seem want-
ing on this subject.

Though the lungs appear to be the great organ of oxygenation in the larger animals, it is well ascertained that a process of nearly the same nature is carried on at the skin; and in many of the smaller or less perfect animals there appears to be no other means for effecting this absorption.

HEATH. See ERICA.

HEAVINESS, in general, the same with weight or gravity. See GRAVITY and WEIGHT.

HEBENSTREITIA, in botany, a genus of the Didynamia Angiospermia class and order. Essential character: calyx emarginate, cleft underneath; corolla one-lipped, lip ascending, four-cleft; stamens inserted into the edge of the border of the corolla; capsule containing two seeds. There are six species, all natives of the Cape.

HECTIC. See MEDICINE.
HEDERA, in botany, English ivy, a ge-

nus of the Pentandria Monogynia class and
Ca-
order. Natural order of Hederaceæ.
prifolia, Jussieu. Essential character: pe-
tals five, oblong; berry five-seeded, sur-
rounded by the calyx. There are six species,
with several varieties.

HEDERACEÆ, in botany, the name of
the forty-sixth order of Linnæus's “Frag-
ments of a Natural Method," consisting of the
ivy, vine, and a few other genera, which from
their general habit and appearance seem
nearly allied. This order consists of herba-
ceous and shrubby plants, most of which,
particularly the ivy and vine just mention-
ed, have creeping branches, that attach
themselves by tendrils to the bodies in their
neighbourhood. The roots are long; the
stems and young branches commonly cy-
lindric. The leaves are alternate, sometimes
simple, as in the ivy and vine; sometimes
winged, as in the zanthoxylum, or tooth-ach
tree, in which the surface of the leaves is
covered with points. On each side of the
foot-stalk of the leaves of the vine are placed
two pretty large stipulæ, or scales; from
the side opposite to the leaves proceeds a
branching tendril, which serves to fasten
the plant to the bodies in its neighbourhood.
The flowers are either hermaphrodite, as in
the ivy and vine; male and female upon
different roots, as in the ginseng; or herma-
phrodite and male upon different roots, as
in the zanthoxylum. The calyx, or proper
flower cup, consists of one leaf divided into
five parts, which are small, and generally
permanent. The petals are commonly five;
but in the cissus four, and in the zanthoxy-
lum none. There are five stamina; but
the cissus has only four. The anthers, or
tops of the stamina, are roundish in the
ivy they are attached to the filaments by
the sides. In the zanthoxylum the filaments
are crowned with twin anthers. The seed
bud is of different shapes; the seed-vessel is
of the berry kind, with one, two, or five
cells, and the seeds are from one to five in
number, placed either in distinct cells, or,
as in the case of the ivy and vine, dispersed
through the pulp without any partition. See
PANAX, &c.

HEDGES, in agriculture, are either planted to make fences round inclosures, or to divide the several parts of a garden. When they are designed as outward fences, they are planted either with hawthorn, crabs, or blackthorn; but those hedges which are planted in gardens, either to surround wilderness-quarters, or to screen the other parts of a garden from sight, are

HEI

may be stayed aftward on. the top-masts are squares.

The heels of HEGIRA, in chronology, a celebrated epocha among Mahometans. See CHRONOLOGY. The event which gave rise to this epocha was the flight of Mahomet from Mecca, with his new proselytes, to avoid the persécution of the Coraischites; who, being then most powerful in the city, could not bear that Mahomet should abolish idolatry, and establish his new religion. This flight happened in the fourteenth year after Mahomet had commenced prophet: he retired to Medina, which he made the place of his residence.

HEIGHT, in geometry, is a perpendicular let fall from the vertex, or top, of any right-lined figure, upon the base or side subtending it. It is likewise the perpendicular height of any object above the horizon; and is found several ways, by two staffs, a plain mirror, with the quadrant, theodolite, or some graduated instrument, &c. The measuring of heights or distances is of two kinds: when the place or object is accessible, as when you can approach to its bottom; or inaccessible, when it cannot be approached. See SURVEYING.

HEIR, in law, is he to whom lands, tenements, hereditaments, by the act of God and right of blood, descend of some estate of inheritance.

HEIR apparent. No person can be heir in fact until the death of his ancestor; yet he who stands nearest in degree of kindred to the ancestor, is called even in his lifetime, heir apparent.

And the law takes notice of an heir apparent, so far as to allow the father to bring an action of trespass for taking away his son and heir, the father being guardian by nature to his son, where any lands descended to him.

The heir, heir general, or heir at common law, is he who after his father's or ancestor's death has a right to all bis land, tenements, and hereditamen's; but he must be of the whole blood, not a bastard, alien, &c. None but the heir general, according to the course of the common law, can be heir to a warrantry, or sue an appeal of the death of his ancestor.

A custom in particular places varying the rules of descent at common law is good, such is the custom of gavel-kind, by which all the sons shall inherit, and make but one heir to their ancestor. The general custom of gavel-kind lands extends to sons only, but a special custom, that if one brother

herit, is good.
die without issue, all his brothers may in-

To prevent injury to creditors by the
alienation of the lands descended, &c. and
depriving them of their claim on the lands,
it is enacted by 3 and 4 William and Mary
c. 14, that in all cases, where any heir at
law shall be liable to pay the debt of his
ancestor, in regard of any lands, tene-
ments, or hereditaments descending to him,
and shall sell, alien, and make over the
same before any action brought or process
sued out against him, such heir at law shall
action or actions of debt to the value of
be answerable for such debt or debts in an
the said land so by him sold, alienated, or
made over; in which case all creditors shall
be preferred, in the same order as in ac-
tions against executors and administrators,
and such execution shall be taken out upon
any judgment or judgments so obtained
against such heirs, to the value of the said
land, as if the same were his own proper
debts; saving that the lands, tenements,
and hereditaments, bona fide aliened before
Provided, that where
the action brought shall not be liable to
any action of debt upon any specialty, is
such execution.
brought against any heir, he may plead
riens per descent at the time of the original
and the plantiff in such action may reply,
writ brought, or the bill filed against him;
that he had lands, tenements, or heredita-
ments from his ancestor before the original
writ brought, or the bill filed; and if upon
issue joined thereupon, it be found for the
plantiff, the jury shall inquire of the value
of the lands, tenements, or hereditaments,
so descended, and thereupon judgment
shall be given, and execution shall be
awarded as aforesaid; but if judgment be
action, confessing the assets descended, or
given against such heir, by confession of the
upon demurrer, or nihil dixit, it shall be
for the debt and damages, without any
writ to enquire of the lands, tenements, or
hereditaments so descended.

Before this statute, if the ancestor had devised away the lands, a creditor by specialty had no remedy, either against the enacted, that all wills and testaments, limiheir or devisee. But by this statute it is tations, dispositions, or appointments, of or concerning any manors, messuages, lands, tenements, or hereditaments, or of any rent, profit, term, or charge out of the same, whereof any person at the time of his decease shall be seised in fee-simple, posses sion, reversion, or remainder, or have power