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phical usually called sea-charts, are projections of some they will diminish and cease. During this fermenta

Hydro! part of the sea, or coast, for the use of navigation. In tion, the barrel must be filled up occasionally with phyllure Hydromel, these are laid down all the rhumbs or points of the more of the same kind of liquor of honey, some of

compass, the meridians, parallels, &c. with the coasts, which ought to be kept apart on purpose to replace
capes, islands, rocks, shoals, shallows, &c. in their pro- the liquor which Aows out of the barrel in frotb.
per places and proportions.

When the fermentation ceases, and the liquor has be-
HYDROGRAPHY, the art of measuring and come very vinous, the barrel is then to be put in a
describing the sea, rivers, canals, lakes, &c. With cellar and well closed. A year afterwards the mead
regard to the sea, it gives an account of its tides, will be fit to be put into bottles.
counter-tides, soundings, bays, gulfs, creeks, &c.; as The vinous hydromel or mead is an agreeable kind
also of the rocks, shelves, sands, shallows, promonto. of wine : nevertheless it retains long a taste of boney,
ries, harbours; the distance and bearing of one port which is unpleasing to some persons; but this taste it
from another; with every thing that is remarkable, is said to lose entirely by being kept a very long time.
whether out at sea or on the coast.

The spirituous fermentation of honey, as also that
HYDROLEA, a genus of plants belonging to the of sugar, and of the most of vinous liquors, when it is
pentandria class, and in the natural method ranking very saccharine, is generally effected with more difficol.
with those of which the order is doubtful. See Bo. ty, requires more heat, and continues longer, than that
TANY Inder.

of ordinary wines made from the juice of grapes; and
HYDROMANCY, a method of divination by wa- these vinoua liquors always preserve a saccharine taste,
ter, practised by the ancients. See DivinaTiON, N° 7. which shows that a part only of them is become spiri.

HYDROMEL, honey diluted in nearly an equal tuous.
weight of water. When this liquor has not fermented, HYDROMETER, an instrument to measure the
it is called simple hydromel; and when it has under gravity, density, &c. of water and other duids. For
gone the spirituous fermentation, it is called the vinous an account of different hydrometers, see HYDRODY-
hydromel or mead.

Honey, like all saccharine substances, vegetable or HYDROMPHALUS, in Medicine and Surgery,
animal, is susceptible of fermentation in general, and a tumor in the navel, arising from a collection of wa.
particularly of the spirituous fermentation. To in- .
duce this fermentation, nothing is necessary but to di. HYDROPHANES, or OCULUS MUNDI, a kind
lute it sufficiently in water, and to leave this liquor of precious stone, which becomes transparent in water,
exposed to a convenient degree of heat. To make much esteemed by the ancients.
good vinous hydromel or mead, the whitest, purest, HYDROPHOBIA, an aversion or dread of water :
and best tasted honey must be chosen ; and this must a terrible symptom of the rabies canina; and which bas
be put into a kettle with more than its weight of wa- likewise been found to take place in violent inflamma-
ter : a part of this liquor must be evaporated by boil. lions of the stomach and in hysteric fits. See MEDICINE
ing, and the liquor scummed, till its consistence is

such that a fresh egg shall be supported upon its sur.

HYDROPHYLACIA, a word used by Kircher
face without sinking more than half its thickness into and some others who have written in the same system,
the liquor ; then the liquor is to be strained and pour- to express those great reservoirs of water which he
ed through a funnel into a barrel : this barrel, which places in the Alps and other mountains for the supply
ought to be nearly full, must be exposed to a heat as of rivers which run through the several lower countries.
equable as is possible, from 20 to 27 or 28 degrees of This he makes to be one of the great uses of mountains
Mr Reaumur's thermometer, taking care that the in the economy of the universe.
bung-hole be slightly covered, but not closed. The HYDROPHYLLAX, a genus of plants belonging
phenomena of the spirituous fermentation will appear to the tetrandria class. See BOTANY Inder.
in this liquor, and will subsist during two or three HYDROPHYLLUM, WATER-LEAF, * genus of
VOL. XI. Part I.






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Hydro- plants belonging to the pentandria class, and in the na- curate and sensible hygrometer by means of a hempen Hygromephyllun tural method ranking with those of which the order is cord of a considerable length, I quickly found, that doubtful. See BOTANY Index.

thongh it was more than sufficiently susceptible of eveHygrone

HYDROPS, in Medicine, the same with DROPSY. ry change in the bumidity of the atmosphere, yet the

HYDROSCOPE, an instrunient anciently used for cord was upon the whole in a continual state of length. measuring time.

eping. Though this change was the greatest at first, The hydroscope was a kind of water-clock, consist yet it did not appear probable that any given time ing of a cylindrical tube, conical at bottom : the cy- would bring it to a certainty; and furthermore, ic linder was graduated, or marked out with divisions, to emed, that as the cord grew more determinate in which the top of the water becoming successively con- mean length, the alteration by certain differences of tinuous, as it trickled out at the vertex of the cone, moisture grew less. Now, as on considering wood, pointed out the hour.

catgut, paper, &c. there did not appear to be a likeHYDROSTATICS, is that branch of physics which libood of finding any substance sufficiently sensible of treats of the weight, pressure, and equilibrium of Auids. differences of moisture that would be unalterable under See HYDRODYNAMICS.

the same degrees thereof; this led me to consider of a HYDROTHORAX, a collection of water in the construction which would readily admit of an adjustbreast. See MEDICINE Index.

ment; so that, though the cord whereby the instru-
HYDRUNTUM, in Ancient Geography, a noble ment is actuated may be variable in itself, both as to
and commodious port of Calabria, from which there absolute length, and difference of length ander given
was a shorter passage to Apollonia (Pliny). Famous degrees of moisture, yet that, on supposition of a ma-
for its antiquity, and for the fidelity and bravery of its terial departure from its original scale, it might be
inhabitants. Now Otranto, a city of Naples, at the readily restored thereto; and, in consequence, that any
entrance of the gulf of Venice. E. Long. 19. 15. N. Number of hygrometers, similarly constructed, might,
Lat. 40. 12.

like thermometers, be capable of speaking the same
HYEMANTES, in the primitive church, offend language.
ers wlio had been guilty of such enormities, that they The two points of heat the more readily determia
were not allowed to enter the porch of the churches nable in a thermometer, are the points of freezing and
with the other penitents, but were obliged to stand boiling water. In like manner, to construct hygrome-
without, exposed to all the inclemency of the wea- ters which shall be capable of agreement, it is necessa-

ry to establish two different degrees of a moisture which
HYGEIA, in Mythology. See HEALTH.

shall be as fixed in themselves, and to wbich we can HYGIEINE, Yyacım (formed of uyins, “ sound, have recourse as readily and as often as possible. healthy''), that branch of medicine which considers “ Ono point is given by making the substance perhealthi

, and discovers proper means and remedies, with fectly wet, which seems sufficiently determinable ; the their use, in the preservation of that state.

other is that of perfect dry, which I do not apprehend The objects of this branch of medicine are, the non- to be attainable with the same precision. A readiness, naturalem See Diet, EXERCISE, &c.

to imbibe wet, so that the substance may be soon and HYGILINE, more largely taken, is divided into three fully saturated, and also a facility of parting with its parts; prophylactice, which foresees and prevents dis- moisture on being exposed to the fire to dry, at the eases; synteritice, employed in preserving health ; and same time, that neither immersion, nor a moderate analeptice, whose office is to cure diseases, and restore exposition to the warmth of the fire, shall injure its health.

texture, are properties requisite to the first mover cf
HYGROMETER, an instrument for measuring such an hygrometer, that in a manner exclude all sub-
the degrees of dryness or moisture of the atmosphere, stances that I am acquainted with, besides hempen and
in like manner as the barometer and thermometer mea- flaxen threads and cords, or substances compounded of
sure its different degrees of gravity or warmth.

Though every stance which swells in moist, and · Upon these ideas, in the year 1758, I constructed
shrinks in dry weather, is capable of becoming an hy- two hygrometers as nearly alike as possible, in order
grometer; yet this kind of instrument is far from be- that I might have the means of examining their agree.
ing as yet arrived at such a degree of perfection as the ment or disagreement on similar or dissimilar treat.
barometers and thermometers. There are three gene. ment. The interval or scale between dry and wet I

ral principles on which hygrometers have been con- divided into 100 equal parts, which I' call the degrees Hygrome.

structed. 1. The lengthening and shortening of strings of this hygrometer. The point of o denotes perfect ters of by dryness and moisture, or their twisting and untwist- dry; and the numbers increase with the degrees of three kinds. ing by the same. 2. The swelling and shrinking of moisture to 100, which denotes perfect wet.

solid substances by moisture or dryness ; and, 3. By 6. On comparing them for some time, when hung
the increase or decrease of the weight of particular bo- up together in a passage or staircase, where they would
dies whose nature is to absorb the humidity of the at- be very little allrcted by fire, and where they would

be exposed to as free an air as possible in the inside of Smeaton's.

1. On the first of these principles Mr Smeaton con- the house, I found that they were generally within one structed an hygrometer greatly superior to any that trad degree, and very rarely differed two degrees; but as appeared before ; and of which the following account these comparisons necessarily took up some time, and is given in the 62d volume of the Philosnphical Trans- were frequently interrupted by long avocations from actions.

home, it was some years before I could form a tolerable Having some years ago attempted to make an ac- judgment of them. One thing I soon observed, nos


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Hygromne altogether to my liking, which was, that the flaxen is kept steadly and the cords strained by the weight, Hygrome

cords made use of seemed to make so much resistance with very little friction or burthen mpon the central
to the entry of small degrees of moisture (such as is stud K.
commonly experienced within doors in the situation Fig. 5. is a parallelogram of plate-brass, to keep Fig. j.
above mentioned), that all the changes were comprised out dust, which is attached to the upper edge of the
within the first 30° of the scale; but yet, on exposing box.cover H ; and serves to shut the part of the hoxe
them to the warm steam of a wash-house, the index cover necessarily cut away, to give leave for the wire
quickly mounted to 100. I was therefore desirous of GI to traverse with the sliding stud nearer to or fur-
impregnating the cords with something of a saline na. ther from the centre of the index K; and where, in
ture, which should dispose them more forcibly to at. fig. 5. a is a hole of about an inch diameter, for the
tract moisture ; in order that the index might, with the wire GI to pass through in the rising and falling of the
ordinary changes of the moisture in the atmosphere, tra- index freely without touching ; b is a slit of a lesser
vel uver a greater part of the scale of 103. How to do size, suflicient to pass the wire, and admit the cover to
this in a regular and fixed quantity, was the subject of come off without deranging the cord or index ; cc are
many experiments and several years interrupted in- two small screws applied to two slits, by which the
quiry. At last I tried the one hereafter described, plate slides lengthwise, in order to adapé the hole o
which seemed to answer my intention in a great mea- to the wire GI, at any place of the stud I upon the
sure ; and though upon the whole it does not appear index KL.
probable that ever this instrument will be made capable 1. In this construction, the index KL being 12
of such an accurate agreement as the mercurial ther- inches long, 4 inches from the extreme end are filed so
mometers are, yet if we can reduce all the disagree. narrow in the direction in which it is seen by the eye,
ments of an hygrometer within oth part of the whole that any part of these four inches lying over the divi.
scale, it will probably be of use in some philosophical sions of the scale, becomes an index thereto. The scale
inquiries, in lieu of instruments which have not yet itself slides four inches, so as to be brought under any
been reduced to any common scale at all.

part of the four inches of the index attenuated as above
Plates “ Fig. 1. and 2. ABC is an orthographic delinea- mentioned.
CCLIXV?. tion of the whole instrument seen in front in its true “ 2. The position of the directing piece RR is so
ig. 1. & 3. proportion. DE is that of the profile, or instru- determined as to be parallel to a right line drawn through

ment seen edgewise. FG in both represents a flaxen o upon the scale, and the centre K of the index ; con-
card about 35 inches long, suspended by a turning peg sequently, as the attenuated part of the index forms a
F, and attached to a loop of brass wire at A, which part of a radius or right line from the same centre, it
goes down into the box cover H, and defends the in- follows, that whenever the index points to o upon the
dex, &c. from injury; and by a glass exposes the scale scale, though the scale is moved nearer to or further
to view.

from the centre of the index, yet it produces no change
“ Fig. 3. shows the instrument to a larger scale, the in the place to which the index points.
upright part being shortened, and the box-cover re- " When the divided arch of the scale is at 10 inches
moyed ; in which the same letters represent the same from the centre (that is, at its mean distance); then
parts as in the preceding figures ; GI are two loops the centre of the arch and the centre of the index are
or long links of brass wire, which lay bold of the in- coincident. At other distances, the extremes of which
dex KL, moveable upon a small stud or centre K. The are eight or twelve inches, the centre of the divisions,
cord FG is kept moderately strained by a weight and the centre of the index pointing thereto, not be-
M of about half a pound avoirdupois.-It is obvious, ing coincident, the index cannot move over the spaces
that, as the cord lengthens and shortens, the extreme geometrically proportionable to one another in all si-
end of the index rises and falls, and successively passes tuations of the scale ; yet the whole scale not exceed-
over N 2 the scale disposed in the arch of a circle, and ing 30° of a circle, it will be found on computation,
containing 100 equal divisions. This scale is attached that the error can never be so great as rögth part of
to the brass sliding ruler QP, which moves upon the the scale, or 1° of the hygrometer; which in this in.
directing piece RR, fixed by screws to the board, which strument being considered as indivisible, the mechani-
makes the frame or base of the whole; and the scale cal error will not be sensible.
and ruler NQP is retained in any place nearer to or “ The cord here made use of is flax, and between
further from the centre K, as may be required by the oth and oth of an inch in diameter ; which can be
screw S.

readily ascertained by measuring a number of turns
“ Fig. 4. represents in profile the sliding piece and made round a pencil or small stick. It is a sort of cord
stud I (fig. 3.), which traverses upon that part of the used in London for making nets, and is of that par.
index next the centre K; and which cao, by the two ticular kind called by net-makers flaxen three-threads
screws of the stud, he retained upon any part of the laid. A competent quantity of this cord was boiled
index that is made parallel ; and which is done for in one pound avoirdo pois of water, in which was put
three or four inches from the centre, for that purpose. two pennyweights troy of common salt ; . the whole
The stud is filed to the edges, like the fulcrum of a was reduced by boiling to six ounces avoirdupois,
scale-beam; one being formed on the under side, the which was done in about half an hour. As this ascer-
other on the upper, and as near as may be to one tains a given strength of the brine, on taking out the
another. A book formed at the lower end of the cord, it may be supposed that every fibre of the cord
wire-loops CI, retains the index, by the lowermost is equally impregnated with salt. The cord being
edge of the stud; wbile the weight M hangs by a small dried, it will be proper to stretch it; which may be
book upon the upper edge : by these means the index done so as to prevent it from untwisting, by tying

A 2

Fig. 3•

Fig. 4.




Hygronc. three or four yards to two nails against a wall, in an untwisting of the string A by the different changes of Hygrome

horizontal position, and hanging a weight of a pound the air, the lower card G, from the mechanical prin- .
or two to the middle, so as to make it form an obtuse ciples of motion, will describe 10 revolutions for one
angle. This done for a week or more in a room, will of the upper card F; or when the lower card G has
lay the fibres of thie cord close together, and prevent made one revolution, the upper card F will bave de-
its stretching so fast after being applied to the instru- scribed but the roth part, or one of its divisions.
ment as it would otherwise be apt to do.

From whence it appears, that by the assistance of the
“ The hygrometer is to be adjusted in the following upper card F, an index is thereby obtained of the num-
manner. The box-cover being taken off to prevent its ber of revolutions the lower card G performs, which
being spoiled by the fire, and choosing a day natu- are reckoned by the line E on the slip of wood.
rally dry, set the instrument nearly upright, about a Example. It must first be observed what division of
yard from a moderate fire ; so that the cord may be- the card F the line is against, suppose 3 ; and also
come dry, and the instrument warm, but not so near what division of the lower card G is cut by the same
as would spoil the finest linen by too much heat, and line, suppose 10: it then appears, that the state of the
yet fully evaporate the moisture; there let the instru. bygrometer is thus, 3 degrees and 10 hundredths of
ment stay till the index is got as low as it will go ; another. If the whole 10 divisions of the card have
now and then stroaking the cord betwixt the thumb passed the line E, the lower card G will have revolved
and finger downwards, in order to lay the fibres there- 10 times, or 10 hundred parts, equal to 1000; the ac.
of close together; and thereby causing it to lengthen curacy to which the principle of this simple contrivance
as much as possible. When the index is thus become answers. Before use, the hygrometer should be adjust-
stationary, which will generally happen in about an ed; to do which, the cards F and G are first set to the
hour, more or less as the air is naturally more or less line E at the o of each, or commencement of the gra-
dry, by means of the peg at top raise or depress the duations : whatever direction the cards afterwards take,
index, till it lies over the point o. This done, remove it must evidently be from the change to greater mois.
the instrument from the fire; and having ready some ture or dryness in the air; and they will accordingly
warm water in a tea-cup, take a middling camel's hair point it out.
pencil, and dipping it in the water, gently anoint the On this principle, but with a degree of ingenuity saussure's
cord till it will driok up no more, and till the index and pains perhaps never before employed, an hygrome-
becomes stationary and water will have no more effect ter has been constructed by M. de Saussure, professor
upon it, which will also generally happen in about an of philosophy at Geneva. In bis Essais sur l'Hygro-
hour. If in this state the index" lies over the degree metrie, in 4to, 1783, is an important detail on the sub-
marked 100, all is right : if not, slack the screw S, ject of hygrometry; from which the following descrip-
and slide the scale nearer to or further from the centre, tion of his hygrometer is taken. The author found by
till the point 100 comes under the index, and then the repeated experiments, that the difference between the
instrument is adjusted for use : but if the compass of greatest extension and contraction of a hair, properly
the slide is not sufficient to effect this, as may proba- prepared, and having a weight of about three grains sus-
bly happen on the first adjustment, slack the proper pended to it, is nearly as of its whole length; that is,
screvys, and move the sliding stud I nearer to or fur- 3f, or 31 lines in a foot. This circumstance suggested
ther from the centre of the index, according as the the idea of a new hygrometer: and, in order to render
angle formed by the index between the two points of those small variations perceptible and useful, the follow-
dry or wet happens to be too small or too large for ing apparatus was constructed.
the scale."

Fig. 7. is a representation of the whole instrument, Fig. 7. Coventor's Ou this principle, a simple hygrometer has been .

with the bair and other appendages complete. The
made by Mr Coventry of Southwark, London. It is lower extremity of the hair ab is held by the chaps
not upon the most accurate constructiou, yet will act of the screw pincers b. These pincers are represented
very sensibly in the common changes of the air. Fig. 6. aside at B : by a screw at its end, it fastens into the
represents the hygrometer as applied to a wall or board. nut of the bottom plate C. This nut of the plate turns
A is a string of whip-cord, catgut, &c. of any length independently of the piece that supports it, and serves
at pleasure : it is suspended on a bracket B, and kept to raise or depress the pincers B at pleasure.
extended by a weight at the bottom C. DD is a slip The upper

extremity a of the hair is held by the
of wood, which with the bracket is fixed perpendicu- under chaps of the double pincers a, represented aside
larly to a wall or side of a room. It has a straight at A. These pincers fasten the hair below, and above
line E drawn down in the middle of the board, ser. fasten a very fine narrow slip of silver, carefully an-
ving to point out the divisions upon the edges of the nealed, which rolls round the arbur or cylinder d, a se.

two thin circular cards F and G. At the centre of parate figure of which is shown at DF. This arbor,
the bottom of each of these cards is glued a piece of

which carries the needle or index ee, or E in the sepa.
cork, through which the string A is drawn: These rate figure, is cut into the shape of a screw; and the
cork pieces serve to preserve the horizontal position of intervals of the threads of this screw have their bases
the cards. The upper card F is divided into 10 equal fat, and are cut squarely so as to receive the slip of
parts or divisions, and the under card G into 103 equal silver that is fastened to the pincers a, and joined in this
parts; the string A being measured into 10 equal manner with the hair.

M. Saussure observes, that hair parts, from the point of suspension H to the surface alone fixed immediately to the arbor would not do; for it of the lower card I. The card F is hung at the first curled upon it, and acquired a stiffness that the counter. part, from H; and the card G at the soth part from poise was not able to surmount. The arhor was cut io the same point: consequently, from the twisting and a screw form, in order that the slip of silver in wind

Fig. 6.


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