Page:Cyclopaedia, Chambers - Volume 1.djvu/1034

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HYDROPIC, a dropfkal Patient ; or a FaTon fwell'd and bloated with the Abundance of Water or Wind. See Dropsy. .

The Word is form'd of J%, Water, and o4fi Maes, Face.

HYDROPS, in Medicine. Sec Dropsy.

The Word is originally Greek, iJ&li, °f "-N aIK ' *k'

HYDROPS ad Matulem, a Term fometimes ufed tor a ^Diabetes. See Diabetes.

HYDROPOTES, in Medicine, are fuch as drink nothing but Water. See Water.

It has Ion," been controverted among Phyucians, whether or no the Hydropotes live longer than other Perfons. See Drink. ,..

The Word is Greek, SA&mru, °f "'""Pi Water, and tow, 1>om; Drinker, of ot», bibo, I drink.

HYDROSCOPE, an Inftrument anciently uled tor the mcafurino of Time. See Chronometer.

The Hydrofcope was a Kind of Water-clock ; confuting of a cylindrical Tube, Conical at Bottom : The Cylinder ■was Graduated, or mark'd out with Divifions, to which the Top^of the Water becoming fucceffively contiguous, as it trickled out of the Vertex of the Cone, pointed out the Hour. „, . c ,.

Synefus defcribes the Hydrofcope at large in one of his Letters. See Clepsydra.

The Word is Greek, vfynfrmt, formd ot uJiif, Water, and truousa, I view, I confider. '

HYDROSTJM'ICAL Ballance, a kind of Ballance con- triv'd for the eafy and exaft finding the Specific Gravities of Bodies both Liquid and Solid. See Specific Gravity.

The Inftrument is of conftderable Ufe in eftimating the Degree of Purity of Bodies of all Kinds ; the Quality and Richnefs of Metals, Ores, Minerals, lie. the Proportions in any Mixture, Adulteration, or the like : Of all which, the Specific Weight is the only adequate Judge. See Weight, Metal, Gold, Mixture, Be. .

The Hydroftatica! Ballance is founded on this Theorem of Archimedes,' That a Body heavier than Water, weighs lefs in Water than in Air, by the Weight of as much Water as is equal to it in Bulk. — Whence, if we fubflraa the Weight of the Body in Water from its Weight in Air, the Difference gives the Weight of as much Water as is equal in Magnitude to the Solid propos'd.

Having, therefore, two Bodies, the one firm, the other fluid, together with the Weight of each apart ; to find their Proportion, divide the greater by the leffer, the Quotient compar'd to one that is an Unite, will be the Antecedent of the Proportion defir'd. -

The Inftrument, with all its Apparatus, is reprefented Tab. Hydroftaticks, Fig. 34. and needs little Defcription.

To ufe it, the Weigh'? E are fo adjufted, as to ballance what is to be hung on the other End of the Beam ; in which State the Inftrument is ready for Application.

Now, to fad the Specific Gravity of a Fluid.— Hang to the other End of the Beam the little Scale F, and to the Bono.- of the Scale the Bubble G ; then fill a Cylindrical Veflel O P about two Thirds with common Water ; and when the Bubble is let into it, the Beam will remain in an horizontal Pofi'ion if the Water be of the fame Specific Gravity as that in which the Bubble was adjufted : If it be not, there will be a Variation ; which is to be corrected by means of little Weights for that Purpofe. ■

Havin" thus adjufted the Bubble in that Water, the Spe- cific Gravity of any other Fluid will be found by weighing the Bubble therein ; and fince you always weigh fo much of the Liquid as is equal to the Bulk of the Bubble, if there be any Variation between fuch Quantity, and the like Quantity of Water, it will be difcover'd by putting Weights into the afcending Scale.

2°. To find the Specific Weight of a Solid. — Inftead of the" Bubble, hang on the Bucket HIK, and the Beam will be in jEquilibrio': Put the Solid intended to be examin'd therein, and counter-poifc it with Weights in the other Scale : This done, note the Weight, and disburthen the Scales of the Solid and its Counter poife, and fink the Bucket into the_ Glafs of Water. — Then, as the Bucket will lofe as much of its Weight, as is the Weight of an equal Bulk of Water ; add the Scale R upon the Patt, which will bring all to an JEquilibrium. — Laftly, Put the Solid into the Bucket, and counter-poife it again with Weights ; and as it anfwers in its Proportion to Water, it may be judg'd either genuine or adul- ter? re, by comparing it to a Standard of that Species of Bo- dies" to which it is fuppofed to belong.

HYDROSTATICKS, the Docfrine of Gravitation in Fluids ; or that Part of Mechanicks which cohfiders the Weight or Gravity of fluid Bodies, particularly Water ; and of folid Bodies immerg'd therein. See Gravity and Gra-

VITATION.

To JlvdroJItttichs belong whatever relates to the Gravities and Equilibria of Liquors ; with the Art of weighing Bodies in Water, in order to eftimate their Specific Gravities. — Mr. Boyle has apply'd ITydrcf.aticks to good Purpofe, in exa-

mining and proving the Goodneis and Purity of Metals, Minerals, and other Bodies, particularly Fluids, in an exprefs Treatife, entitled, Medicina Hydroftatica. See Hydrosta- tic a l Ballance.

The Word is Greek, compos'd of tfjtyi, Water, and rami), Staticks, of tot©-, fans, Handing, of t<r»(u, fo, jifto, I Hand I flop : Hydrofaticks being conceiv'd as the Docfrine of the E- quilibrium ot Liquors. See Equilibrium and Staticks.

The Laws of Hydrostaticks, mtb the Application thereof; fee deliver 'd at targe under the ArticlesVt.vijs and Specific Gravity.

Hydrofaticks are frequently confounded with Hytraulicks, by reafon of the Affinity of the Subjects ; and feverai Au- thors chufe to treat of the two promifcuoufly. See H\- draulicks.

The eldeft Writer on Hydrofaticks is Archimides, who firft deliver'd the Laws thereof in his Book de infidenttbtts Tmmida. Marin. Gletaldus firft brought his Doctrines to Experiment, in his Archimedes fromotus : And from him Mr. Oughtred took the greateft Part of what he has given us on this Subject. Monf. Mariotte, in a French Treatife, publifli'd at 'Vans in i«8t), Of the Motion of Water and other Fluids, gives moil of the Propositions of Hydrofaticks and Hydraulicks, prov'd by Reafon, and confirm'd by Experiments : Nor are Mr. Boyle's Hydreflatical 'Jfaredoxes, and Medicina Hydroftatica, to be overlook'd : The J'efuit Fr. Terthts de Lanis, in the Hid Tome of his Magtprium Nature 1$ Artts, lays down the Doctrines of Hyaroflaticks more amply than they are elfewhere found. F. Lamy, in the 2d Patt of his Me- chanicks, entitled, Traite de I'Equilibre des Liqueurs, deli- vers the fundamental Laws of Hydrofaticks, and Hydrau- licks ; and the like is done by Dt.'Wallis, in his Mechamca. Laftly, Sir If. Newton gives fbme of the fublimcr Mattets in the 2d Book of his •Pbilofcf'h. Nat. 'Princip. Mathemat.

HYDROTICKS, in Medicine, Sudorifcks 5 or Remedies that promote Sweat. See Sudorificks.

The Word is Greek, form'd of Hty, aqua, Water.

HYGIEINA, that Branch of Medicine which confiders Health ; and difcovers proper Means and Remedies, with their Ufe, in the Prefervation and Recovery of that State. See Medicine and Health.

The Objects of this Branch of Medicine are the Non- Naturals: See Non-Naturals.

Hygieina may be divided into three Parts ; Propbylaffice, which forefees and prevents Diieafes 5 Synteritice, employ'd in preferving Health ; and Anltleptice, whofe Office is to cure Difeafes,and rcftore Health. See Prophylactice,0?c.

The Word is Greek, T>ara, of iyh, found, healthy.

HYGROCYRSOCELE, in Medicine, a Branch of a Vein fwell'd with ill Blood, ot other Humours. See Varex.

The Word is compos'd of uy&f, hwnidus, and ta>ztnxx,h)i, or rather */? tremiAH, ramex varicofus.

HYGROMETER, a Machine or Inftrument whereby to meafure the Degrees of Drynefs or Moifture of the Air. See Air, Humidity, fgc.

The Word is compounded of the Greek, vyeji, humid'.ts moift, and fuT^iat, metier, I meafute. See Hygroscope.

There are divers Kinds of Hygrofcopes ; for, whatever Body either fwells or fhrinks by Drynefs or Moifture, is capable of being form'd into an Hygrometer. — Such ate Woods of moft Kinds, particularly Afh, Deal, Poplar, f£c. Such alfo is a Cat-gut, the Beard of a wild Cat, &c. See Wood, &c.

The beft and moft ufual Contrivances for this Purpofe are as follow :

ConfruSion of a Hygroscope.

Stretch a hempen Cord, or a Fiddle-flring, as AB (Tab. Pneumaticks, Fig. 7.) along a Wall, bringing it over a Truckle or Pulley B ; and to the other Extreme D, tye a Weight E; into which fit a Style ot Index FG— On the fame Wall fit a Plate of Metal H I, divided into any Num- ber of equal Parts : And the Hygrofeope is compleat.

For it is Matter of undoubted Obfervation, that Moiftute fenfibly fhortens the Length of Cords and Strings 5 and that, as the Moifture evaporates, they return to their former

Length : And the like may be laid of a Fiddle-ftring

The Weight, therefore, in the prefent Cafe, upon an Increafe of the Moifture of the Air, will afcend; and, upon a Dimi- nution of the fame, defcend.

Hence, as the Index F G will fhew the Spaces of Afcent and Defccnt ; and thofe Spaces are equal to the Increments and Decrements of the Length of the Cord or Gut ABD ; the Inftrument will difcover, whether the Air be more or lefs humid now, than it was at another given Time.

Or thus : If a mote fenfible and accurate Hygrofeope be requir'd ftrain a Whipcord or Fiddle-flring over fevcral Truckles or Pulleys A, B, C, D, E, F, and G, (Fig. 8.) and proceed with the reft as in the fotmer Example. Nor does it matter whether the feverai Parts of the Cord AB, BC, CD, DE

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