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HEADBORROW, or Headborougii, 
the chief of the frank pledge, and lie that 
had the principal government of them 
within his own pledge. He was called also 
burrowhead, bursholder, third-burrow, ti- 
thing-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 par- 
ticularly the' auditory nerve and membrane. 
See Anatomy and Physiology. 
HEAT. The laws according to which 
the temperature of bodies is subject to in- 
crease or diminution, have been discussed 
in the articles Caloric, Capacity, Cold, 
Combustion, and Chemistry. In the 
first of these articles, caloric was consider- 
ed as a substance capable of passing from 
body to body, and subsisting in them in 
different states. This is the general doc- 
trine 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. Ca- 
vendish, Dr. Young, and Count Rumford. 
“Ifheat," saysDr.Young,“whenattached 
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 communi- 
cated by contact, when the end of a tuning- 
fork is placed on a table, or on the sound- 
ing-board of an instrument, which receives 
from the fork an impression that is after- 
wards propagated as a distinct sound. And 
$he effect ofjradiant heat, in raising the 
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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 mote 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 direct- 
ly made out. It would carry us too far into 
physiological disquisition, if we were to pro- 
ceed 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 
