James Orr.

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cles, varying from five to twelve In number. Is situated at the opposite end. Tliese
tentacles are exceeding coniractlle, at one moment thrown oot as kmg delicate
threads, at tho next, drawn up Into mlnnte wart-like khoba. Nomerons thread-cells
project from tlielr surface, the larger ones possessing a sheath and throe recorred
darts or barhs, and terminating in a long and extremely slender filament, Tlie
month le.ids Into a capacious cavity, excavated throughout the whole length nf the
animni, which, exclusive of Its tentacles, seldom exceeds three-fourtfas of an inch.
On minutely examining the H., or any member of the class Hjrdroaoa, the ho iy Is
found to he composed of two membranes, an ectoderm aijd an cndoderm,the former
coiistitnting the outer layer of the animal, and havlui? one side always in contact
with the wuter, while the other side is in close contact with the endoderm, whose
free snrfnce forms the lining of the groat internal cavity. The food of the H. con-
sists of snch minute living organisms as come within the reach of Its tentacles,
and l)y these apparently fragile threads, which the animal projects llkealasao, eras-
taceaus, vi'orms, &c^ are seised, which would be deemed at firet sight superior to
their captor in strength and activitr. Ttie tentacles appe:ir, however, to potciesa,
through the action of the thread-cells, a powerful benuinmng and paralysine iiiflu-
ence, for It iioa been observed that soft-bodied animals which have sncceeded in es-
caping from the grasp of the H. frequently die very shortly. The prey, when
mastered, but often when still alive. Is thrust into the Intcmnl cavity, where tho
nutritive parts are absorbed by tho H., while the indigestible portions are expelled
through the mouth.

Althongh the H. is usually found adhering by Its circular foot or disc to snb-
mersed leaves, twigs, &c., it is not permanently fixed. It often moves on sarfaoes
under water soniewliat after the manner of a leech, both ends taking a part in tlie
movement, and occasionally the disc Is protruded above the water, and thus acta a«

Sometimes, especially in the autumn, true reproductive organs may be observed,
both male and female organs being usually situtitcd on the same animal. Propaga-
tion bv gemmation Is, however, the most common mo<le of increase*. Mintite tuber-
cles appear on the body of the parent animni, which, as they increase in »i«e,
gradnjiliy resemble it; becoming perforated at their free extremity, and tentacle*
gradually being formed. The pedicle by which tliey originate by degrees becomea
thinner, and finallv gives wav, leaving the young H. perfectly independent. One of
the most remarkable points in the history of this animal is its power of being mol-
tiplied by meclianlcai division. If a H. l>e cut into two, or even more pieces, every
one will, in time, assume the form and functions of the original animal.

Several species of H.. such as H. viridiSy H. vulgaris, a. /ttsto, Ac, have bcon
described, which differ in sise, color, Ac. When living hydras are removed from
the water, they appear like minute specks of jelly, wlilcli quickly recover their true
form on being restored to tlieir proper element. The great authority on these
siugnlar animals is Trembley, whose '* M^molres pour servlr k lliistoire d^n Qenre
de Polypes d'eau donees" waa published in 1744.

HY'DNUM, a genns of fungi (Hjfntenomtfeete$)y having the underside of the
fpileiu covered with soft spines wliich bear tiie spores. The species are prottj

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ttumeroiw, M>tn« of thctn BriMfth ; among trhteh Is J^. repaininm, more coimnon in
some pnrts of rhe conliueiit of Kitrope, and inocli o«ed an au escnlont Jti Frnnre,
Itniy, and G«muiny. It grows on tUe gronnd, cbiefljr Su pine and oak vroods, eilkt^r
solftnry, or In clusters or rings.

HYDRA, a fabnloos monster of the nudent world, said to have Inhnhiled the
marshes of Leniiea, In Argolis, not far from the sea-coapt. AccounU vary both us
to its oritrlu and appearance. Some wake it the issqe of Styx and the l*ltan Pall s,
and others, of Echidna and Tvphon. It It represented as liaving several bead?,
which iromodiateljgrew np again ns often ns tlier were cntoff. The nnniltcr gt>n-
cra'.iy ranged from seven to nine, though SImonides gives It lirty, and certtiin his-
torisnfl a bnndred, nnd even morv. Its months, which were as nnmerons ns its
heads, discharged a subtle ni»d deadly venom. The destruction of this reptile was
one of the twelve labors of Hercules (q. t.>.

HY'DRA. The, or Fresh- wntcr Polype, is the trpeof tbe clous Htdbozoa, which,
with the Akthoeoa, form the snb-kingdooi Cctlauarata of recent suologiste. Seo


HYDRA, nni«land of Greece, Is sitnotcd off the eastern shore of the Ptlripon-
n-sns (now the Moreu), sbont 5 miles distant from the coas* of the depnrtnitiit of
Argolis and Corinth. It is abont IS miles long and 8 miles bt-oad, nnd has nn urea
of 88 sqnnrc mll^ llie shores are rocky and steep, and the interior, rising to nbont
1800 feet in hcl«jht, is destitute of vegetation nnd of water. On the north-west const
Is the town and seaport of Hydra, llie white, flnt-roofed houses of wlilch. nsi-ending
from the IUDt>or, climb np the side of a hill. The streets, owing to the Irregnlnrity
of the site, are steep and uneven, Imt reniatlcably clean. This town, the <»nly one
in the island, Is one of the most bcantiful in the whole of Greece. Fop. (1871) 1 1,684,
who are chiefly employed in cotton nnd silk weaving. In tanning nnd In conimerce.

The island of II. was uninhabited in ancient times. Tlic nucleus of the town was
formed by a few fishermen nnd pcaennts who, suffering from the oppresslc n of the
Turks, cros.«cd over from the neighboring mainland and were ■after>vards followed
by crowds from Albania. Argolis nnd Attica, in the 18th and 16th centuries. In the
Grecian war of Indepenacnce the Hydrlotes took a most active pnrt, and none Were
more libeml In their coi.tribntions to the patriotic cause. In 1S25 the population
was estimated at 40,000, and about that lime the islanders were considered the
richest in the archipelago. They possessed exclnsively the cnrrylng-trade of the
Black Sea nnd the Mediterranean, and traded to England, the Baltic, and even
America. Since the revolution, however, more accessible ports have risen to be the
centres of Greek commerce, and H. has considerably declined.

HYDRA'CIDS, or Hirdrogen Acids, a name giv«n to adds in which the acidify-
ing principle was supposed to t)e hvdrogen. See Aoise. The division of acids into
oxyaMds and hydraeids belongs rather to a past tiian to the present state of chem-

HY'DRA GOGUES are those active purgatives which produce a great flux from
the intestinal membrane, and which conseqiiently give rise to very watery stoolji.
They are of extreme use in some of the varieties of dropsy, being the most effi-ctnal
means of dimiulsbiug the liquid poured into the cellular tissue and serous cavities
of the body.

Jalap (especially when combined with bltartrate of potash) and elaterinm, a
medicine which from Its exti^rae power. mn?t be given In very small doses (one-
eighth to one-third of a grain), and with great caution, are perhaps the best ex-
amples of this class of purgatives.

HYDRA'NGEA. a genus of plants of the natnrsl order Hydrangtcuxte, which
many botanists make a sub-order of Saxifragetp,^ distinguished by having 4— C pet-
als, 6 — \% or many stamens, a more or less inferior ovary, and 2—6 styles. Hudran-
geaeecB are shmbs with opposite, or sometimes whorled leaves, destitute of stipules.
in the genus H. the flowers are In cymes, the exterior flowers sterile and dilate<l.
Few species are known, and they are chiefly natives of the southern parts of North
America, and of China and Japan. The species popularly known as the Utdranqea
(A. horUn$ia)f is a native of China and Japan, and has long been In coltivatlou

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thero as an ornamental plant. It wat Introdnced into Britain by Sir Joseph 1
in 1788, and speedily became very popnlar, being readily propagated by lliyeni and
cattiugs, BO 08 to be not only a favorite greeii^lioasc plant, but a frequent omament
of cottage windows. In the soatii of England, It eudnres the open air. It acems
almost Impossible to water it too freely ; a large plant has been known to roodve
with advantage one hnndred (rallous of water daily; and in favorable circumstances
it becomes a magnificent shmb. A plant in Devonshire has had 1000 large cyroee
of flowers expanded at once. xThe flowers, generally pink, ore t^omctiihes bhic ; tho
bine color is owing to pccnliarlti<*s of soil. Peat ana Iron ore are said to be prodnc-
tive of bine flowers in the Hydrangea.— H. Japcnicct, introduced into Enrope
from Japan by Stebold, Is remarkable for its very large cymes of flowers.— fl. fi^MS
and H. axjurcifolia^ American speciea, are not nnfreqneutly to l>e seen in llower-
giirdcns lu North America.

HYDRA'STIS, or WamcriOf a genns of plants of th9 natural order RammerMlactm
alH<Ml to AnenvoiMf but having flowers destitute of petals, and succnleut or baeeaU
fmit, collected into a head. Tlie only known species, H. Canadmsu^ a perennial
herbaceous plant, withtnl>erou8 roots, and head of frnit resembling a rai^berry, b
common in watery places in Canada, and among the Alleghanies, as far aonlh as
Carolina. Its root is i|sed for dyeing yellow, and also in medicine as a tonic Yn^
LOW Root and Oiunob Root ai« its American names.

HY'DRATBS ore substances In which a definite quantity of water is chemically
combined with a definite quantity of some other coustltnenL 'Although water is
o perfectly indifferent substance, possessiug neither acid nor basic properties, yet it
enters into combination l)oth with acids and with l)ases, and thus toriiia the bodies
termed hydrates. Thus, when an acid has once been allowed to combine witb
water, tlie entire separation of the water can usually only be effected by the presence
of some strong base, wliich displaces the water. If, for example, we distu dilated
sulphuric acid, water is expelled up to a certain pointy when both acid and wator are
disiilied together. The liquid now contains one equivalent of water, and one of
acid (HO.SOr), and is termed hydrated sulphuric acid, and this equivalent of wat^
can only be displaced by on equivalent of potash, or some other uase. Hydrate of
baryta (BaO,H6), hydrate of lime or slaked lime (CuO,HO), hydrate of sesnnioxide
. ,' .... ^ „,.,^f. . _.. „ 7 (CuO.UO), f • " ■

of iron (Fe,Os,SHO), and hydrate of oxide of copper (CuO.UO), are similar c
except that here tlie water is displaced by an acid instead of o l>ase. The above are
examples of hydrates of acids and bases or oxides. Gypsum (CaO,SOt,SHO) is an
example of a hydrate of a salt.

HYDRAULIC CRANES have come into very extensive nse within the past few
years. Wherever a large nuinl>er of crones have to be worked near each otJicr,
water>pres8nre is by far the most manoceable, economical, and convenient mode
of working theuL sir W. Armstrong & Co., of Newcastle, have taken the lead iu
this kind of machinery. They have fitted up a great many railway gooda-etatious
with complete systems of hydraulic cranes.

One of the simplest forms of hydraulic cranes, such as ore in use for loading
goods in a railway station, is made entirely.of iron, and cousista of two nprigbt
cheeks. l>etweeii which there Is fixed a hydrau.ic ram (similar to that nsed in the
hydraulic press), occupying the lower half of the tipriglit frame. The npper end of
this ram carries a pulley. A similar pulley is fixed to the upright frame. A
chain is secured to a bracket, on the upright franiu. This chain passes up over
one pulley, down and under the other pulley, and tlien over the pulley on the
end of the jib of the crane. It is obvious that the rising and falling of the ram
will cause tbo chain to ascend and descend with its load.

The ram is forced to ascend by the admission of water nnder great pressure
by the handle, which serves also to allow the water to flow out after it has done
its work, and the ram descends by its own weight, allowing ttie cbaiu to run
down with or without a load on it.

The pressure usually employed in working hydraulic cranes is greatly in excess
of the pressure admissible in the case of steam. Six or seven hundred pounds to
the sqnui-e inch is usually employed as the working- pressnre. It is got up to tlils
great pressure l)y moans of an arrangement culled an accumulator, which consists of
a largo liydranlic ram of 10 or 18 Indies in diameter, carrying a wronjfht-iron cyUo>
der. This cylinder is filled with stones or gra\'el to the weight of 60 or 70 tons. A

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])Owerfal hoffEontAl steam-engine forces water luto ft lower cyjfnder. and slowly
raises the ram. witti its eiionnous load. Pipes lead away from the CTllnder to the
craues in tlie different pans oC the station, and are thns supplied with water under
file grt^t pressnre canscd Ht the load, forcing the ram Into tlie cylinder. The load
is constantly rising and falling n little as the craues draw their sopplivs from the cyl-
imler. If the cranes were supplied direct from tlie force-nam|)s of ttie ctcnm-ensine,
without iho intervention of this accumulator, their action would be jerky ami un-
steady. The accumulator acts as u reservoir of power, and when it hap|>eu8 tliat
a freat number of cranes are drawing off water at the same moment, and in excess
of what the engine force-pumps can snpply, the ram descends, Icecping up tlie while
tiie fnll 700 lbs. pressnre ; and then, when the cranes arc demanding less abundant
supplies, the engine overtalces its work, and scuds the ram up again. When it
arrives at the top. it touches a lever communicating with the ihrot tie-valve of the
engine, and thus slows or stops the engine when the accumulator has mounted to
its mnzimum height. The moment it begins to descend, the lever is relieved,
the throttle- valve opens, and the engine goes on again with soch speed as tiie work

It is easily seen that when the pulley rises any given distance, the weight will, nt
the same time rise double that distance, because ihe pulley raises a double length of
chain; and, in the same wiiy, by passing the chain twice, thrice, or any greater
number of times over pulleys, the weight can be made to travel any number of times
further than the ram. It is, in fact, the reverse action of a block and tackle. If the
block is nmde to move, the fail will move fnrther ihon the block in proportion to
the number of times the rope passes over the sliea\-es. This kind of arrangement
is adopted when it is desired to lift anything to a considerable height, such as grain
to upiier fluors of u warehouse. Tlicre is, of course, a diminution in the weight tie
machine can hoist, in proportion to the excess of travel of the load to that of
the ram.

The hydraulic lifts, or ascending rooms, now In use in many lorgc hotelfi, ore con-
structed on the same plan as the accumulator. A cylinder is sunk 60 or 70 feet into
the ground, thns adrniiting a ram of nearly equal length to rise out of it, on a t>nffl-
cleni pressure of water bemgforced into it by a stean;-engine. The ascending room
takes the place of the loadi'd cylinder. Balance weights are attached to the ascend-
ing room, to steady its movements, and to gnard rgainst any failure in the mechon-
ism. A roi>e passing from bottom to top of the channel, through which the ascend-
ing room rises, ufforas to the person in the room the means of regulating its move-

HYDRAULIC ENGINES are sometimes used where water under liigh pressure
is obtainable. They do not differ in any essential particular from a stcuni-enginp.
As the pressure under which they work Is from five to U-n times greater than tiiat
of a steam-engine, they are much smaller. One form of hydraulic engine is de-
sciit)ed under the head of Wateb-Powbr. Another common foim is that of three
snmll cvlinders in wliicli three plungers work. The water is admitted into the cyl-
inders by means of valvei^ and forces the plungers outwards. These plungers are
connected with n three-throw crank ; and when they have completed their outward
travel, or working-stroke, the wnter is allowed to escape from the cylinder; the
plunger then slioes inwards, to be i^in forced outwards by a fresh rush of water
admrnud at the proper instant into the cylinder by the action of the valve.


HYDRAULIC PRESS, called also Brnmah*s Press, from the name of its In-
ventor, dependH on the principle, that a pressure exerteo on any part of the surface
of a liquid is trnnsmittod nnaiminished to all parts of the mass, and in all direc-
tions. See Hydrostatics. The annexed figure represents the essential parts of
the machine, the details of construction being omitted. F is the caviiy of a strong
metal cylinder ^ into which the piston, D, passes water-tight throngh the top. A
tube, O, lead« c^oin the cylinder to a force-pump H ; nnd by moans of this, water is
driven from tlte tank T Into the caviiy P, so oa to force the piston, D, npw anis. The
piston supports a table on which are placed the holes, 1>ooks, or other artides to be
pressed ; and the rising of the table presses them against the cutablatore AA, which is

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fastened to the pillars B. B. The power of
the prei^s is readily calciilHted. Sappoee
that the pninp ba« only QiK^lbooraudth of
the area of D, and that, by lueaiia of its
leveMiandle, the piston of the pninb is
preyed down with a force of 500 poandis
the piston of the b:irrel will rise with a
force of one ihoiisnnd times SOO ponuds. or
more than WO tons. The rise, boweVer,
will be slow in proportiou to Uie power.
The coormons nmltiplyiiig power kItco by
this niHcliinehaa been employed for a gT««t
variety of useful purposes, such as com-
pressing Imies of cotlou, paper, Jkc, ex-

Kreesiu^ oils, beDduiK iron plates and
ans and raising weights. This was the
ineiiiis emplQved for launching the Grmi
BasUm at Millwall, and for raising to
their position the talics o( tbe Brliaunia

HTDRAULTC RAM, a simplo and coin
▼enieiitJy applied luectianism, by wlilch
tlie momentum or weight of falling water
can be made available for raising a por-
tion of itself to a considerable height. In the annexed figure, which repreaeuts a
section of Montirolfler's hydmolic ram. R is the reservoir from which the water
fulls. RS the height of the fall, and ST tbc boriaoutil tn()e which conducts t he wattT
to the engine ABHTC. E and D are two valven, the former of which closes its
cavitv by ascending, the latter by descending: and FG is a pipe reaching within a
very little of the bottom CB. The valves arc such that the water at iu normal pressure
cannot snpport th-lr weight ; the valve £ is prevented from falling b^-low a certala
point by a knob alwve mn. When the water is allowed to de^Mind from the ro.-^er-
volr, after flUlne the tube BBS, it rushes out at the aporture mtK, till its velocity in
descending RST becomes so great as to force np the valv»{ B, and close the means

of escape. The wat>er being thu9 sad-
denly checked, and unaUe to find a
pastta^e at mtu, will pr(>du<x>a great ac-
tion on ev.-ry part of the contjiining
ve:«sclt>, and by its momentum raise tiic
valve D. A portion of writer being ad-
mitted Into the vessel ABC, the Impulse
of the column of fluid is expended, the
valves D and B fall ; the opening at D
being thus clostxl, and that ut «iu»
opened. Tlfe water now rut^hes ont at
nmae b(*fore. till its motion is agafu
Slopped by its currying np the valve E,
when ihcs op^raffm i? ropeated, tt»o
fluid impulse oiienitig the valve at D,
lhroii;;h which a portion of the water

KISS 8 into ABO. The valves at Eand
thus altcnintely closing and opening,
and water at every opening of D making Its way into ABC. the a'u: therein is oon-
densed, for it has no commnnicatiou with the atmosphere after the M*ater is biglier
than the bottom of the pipe FG. This condensed air, then, exercises great force on
the purfnce, op^ of the water, and raises It in tlie tube, FG, to a height proporUoued
to the elasticity of the imprisoned air. The principles of the hydraulic ram are
susceittibleuf a verv extensive apnlicalion. In well-constructed rams, tlie mechani-
cal effect, obtained has been fonuU to l)e alK)Ut cj of tlie energy of the falling water.
For raising comimratlvely small quantities of water, such as are necessary for the
aupply of smglo uousesi form-yards, Ac.— where water at the lower level iflpleiiUtoi

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and cbetp— the hydraalic mm is a most ivefol piece of inechftnlflin. Its details have
been greutly improved since tlie time of Moutgoifler.

HY'DRID^ a fnmily of serpeDts, sometimes so defiued as to iDcladc iiomer-
ons fresh-water snakes which are not venomons, and sometimes limited to veno-
mous sea-»erpents, inhabiting tlie Indian, f^hineso, and tropicui Auftmliau seas.
These sea-seiiMifits, forming tlie genus Uyarophis (or Budruk)^ and ofiier genera re>
cently sefMinited from it^ have tiie tail coniprnsfed and the belly keeled, so that thi-y
have the power of swimming like eels; They have small heads and small eyes: they
are i-emarkable for the lar^e siae of their nasal shields ; they are generally of a yef-
lowit'i-green color, varied with blackish rings or loseiige-sbaped s|>ots. Their lungs
are often prolonged into a reservoir of air as far as the commencement of the tiiTl.
They are often from two to five feet long. They are frequently seen asleep on the
snrface of tlie sea, and are easily caught in this condition, in which, apparently, thry
often fall a prey to sharks. They are supposed to live on small fishes and cmsto-
ceans. They are sometimes found coilea up among seaweed on the shore, and are
much dreadf d by fliihennen. In some places, thev arc very numerous. One species,
at least, is esteemed good food by tlie Tahiiiaos. iiore than fifty species are known.

DY'DlilDEH. This term is applied both to combinations of hydrogen with met-
als, and to similar combinations witli organic or com)K>nnd radicals. Hydrogen
forms hydrides with at least four metale — vis., arsenic, antimony, copper, and po-
laHHiam. The first two of these are the well-known gases, arHeuinrctied hydro;ren
(AsUji) aud aniimoninretted hydrogen (Sblls). The hydride of nutliyl or marrli-
gas (C2nt,H), aud the hydride of ethyl (C4He,U), are examples of the second
variei y of hy d rides.


IIY'DROUELK (Gr. hydor. water, and ki:i^ a swelling) Is the medl&tl term for a
dropsy of the tpnica vaginalis, a perons nieinbrane or k«c investing the testis.
Hydrocele occurs as n smooth, pear-Bhn|x'd swelling, flnnctuatlug wien pre8s«d,
devoid of pain or teuderue&«<, but sometimes caudug u slight uneasiness Iroia its

The onantity of serous fluid In the sac is usuiUij from six to twenty onnces,but
it ocrasionally exceeds a iiuiidrcd ounces. Hydrocele may occur as a rfsnll of
acnte Inflnmnmtiun. but It most commonly comes on without any apparent local
caupc. Ii is most frequently met with about or beyond the mlditle period of life,
aud generally in pcrsunn of feeble power, or with a tendency to gonl; W)metimes,
however, it occurs in young children, either in the ha me form as in adults, or as
what is termed coru/e/n'to/ Ai^roceJf, when the communication between the tunica
vaginalis and the atKiominal peritoneum is not obliterated, np it normally should be.

The treatment is divided iiito the palliative and the curativs. Bv the former, tiie
surgeon relieves tho present annoyance of his* patient, while by tlie latter he alms at
the permanent removal of the dif^ease. The jMillIative treatment consists in the use
of suspensory bandn'/es, evaporating and dlscutlent lotions, and tapplns with a fine
trochar. Tapping seldom give?* more than temporary relief, the sweuiug usually
again regaining its former bulk in three or four month)*.

The curative treatment consists In setting up sufficient Inflammation In the
tnuica vaginalis to destroy its undue secreting laculiy. This is most commonly

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