Hydroidea 
In some systems of classification it also includes the 
Trachymednsii' and lliidroeoraUinfr. The group Uydro- 
i/i' 'Inxfeof some authors is equivalent to Hydroitlea. Also 
hydrokinetic (hi dro-ki-net'ik), a. [< Gr. Mup 
(Mp-), water, + Kiv'rrriKOf, of moving, < tuveli; 
move.] Pertaining to the motion of fluids. 
Ilifdrokinetic permeability a name for the specific 
quality of a porous solid according to which, when placed 
in a moving frictionless liquid, it modifies the flow. 
Sir C. W. Thomson, Reprint of Papers, 628. 
hydrokinetical (hi"dro-ki-uet'i-kal), a. [< hy- 
ilrokiiirtir + -/.] Same as hydrokinetic. 
hydrokinetics (hi"dro-ki-net'iks), n. [PI. of hy- 
drokinetic: see -/cs.] The mathematical theory 
of the motion of fluids ; the kinetics of fluids, 
in either of the meanings of kinetics. 
Hydrolea (hi-dro'le-a), n. [NL. (Linneeus) (so 
called because growing in wet places), < Gr. 
Mop (Mp-), water, + L. oleum, oil (or Gr. ifai- 
ov, olive-oil, oil).] A genus of dicotyledonous 
gamopetalous plants, of the natural order Hy- 
drophylldcefe, and the type of the tribe Hydro- 
leea'. They have a subrotate 5-cleft corolla, sepals dis- 
tinct in the bud, stamens about the length of the corolla, 
filaments dilated at the insertion, ovary 2- or 3-celled, and 
styles 2 or 3. They are herbs or rarely suffruticose plants 
with ovate or lanceolate entire leaves, which are numerous 
on the stem and often with aspine in the axils, and clustered 
blue or white flowers. About 14 species are known, widely 
distributed in warm countries. Four species are found in 
the southern United States. H. Zeylanica of India has 
bitter leaves, which are beaten into pulp and applied as a 
poultice to sores, with good effect. 
Hydroleacese (hl-dro-le-a'se-e), n.pl. [NL. (R. 
Brown), < Hydrolea H- -acece.] Same as Hy- 
drophyllacea!. 
Hydroleeae (hi-dro-le'e-e), ?. pi. [NL. (R. 
Brown, 1816), < Hydrolea + -ea:.~] A tribe of 
plants of the natural order Hydrophyllacea!, 
containing the single genus Hydrolea. 
hydrolite (hi'dro-lit), n. [< Gr. Mop (Mp-), 
water, + ).iffo$, stone: see -lite.'] The zeolitic 
mineral gmelinite. 
hydrologic (hi-dro-loj'ik), a. [< hydrolog-y + 
-ic.] Of or pertaining to hydrology. 
We . . . consider the forests ... as regulators of hy- 
drolof/ic conditions, influencing the waterflow in springs, 
brooks, and rivers. Pop. Set. Mo., XXXII. 226. 
hydrological (hl-dro-loj'i-kal), a. [< hydro- 
Ionic + -a?.] Same as hydrologic. 
hyidrologist (hi-drol'o-jist), re. [< hydrolog-y + 
-is'f.] One skilled in hydrology. 
hydrology (hi-drol'6-ji), n. [= F. hydroloaie 
= Sp. htdroiogia = Pg. hydrologia = It. idrolo- 
gia, < Gr. Mop (Mp-), water, + -/toyia, < teyuv, 
speak: see -ology.~] The science of water, its 
properties, phenomena, and laws, its distribu- 
tion over the earth's surface, etc. 
hydrolysis (hi-drol'i-sis), n. [< Gr. Map (Mp-), 
water, -t- Atwf, a dissolving, < /ti>ejv, loose, dis- 
solve.] A kind of chemical decomposition by 
which a compound is broken up and resolved 
into other compounds by taking up the ele- 
ments of water. Thus, by hydrolysis cane-sugar takes 
up a molecule of water and is resolved into one molecule 
of dextrose and one of levulose. 
hydrolytic (hi-dro-lit'ik), a. [< hydrolysis 
(-lyt-) + -ic.] Producing hydrolysis, or relat- 
ed to the process or results of hydrolysis. 
Hydrolytic decompositions, that is to say, such as are 
connected with the union of the elements of water with 
the decomposing body. Encyc. Brit., XVII. 671. 
hydromagnesite (hi-dro-mag'ne-sit), n. [< 
Gr. itiup (Mp-), water, + E. magnesia + -zte 2 .] 
A white native hydrous carbonate of magne- 
sium, sometimes occurring in crystals, but 
more frequently amorphous, earthy, and chalk- 
like. 
hydromancy (hl'dro-man-si), n. [= Sp. hidro- 
mancia = It. idromanzia, < L. hydromantia, < Gr. 
as if *Mpo/iavTela (cf . Mp6[unm<;, one who divines 
from water), < Map (Mp-), water, + /tavreia, divi- 
nation.] Divination by some use or from some 
phenomenon of water. 
hydromania (hi-dro-ma'ni-a), n. [< Gr. Map 
(Mp-), water, + fiavia, madness.] Inpathol., a, 
species of melancholia under the influence 
of which the sufferer is led to commit suicide 
by drowning. It sometimes appears in pel- 
hydromantic (hi-dro-man'tik), a. and n. |jAs 
In/dromancy (-mant-) + -/c.] I. a. Pertaining 
to hydromancy. 
If. . The art of producing surprising effects 
dependent on the principles of hydrostatics 
and hydrodynamics. 
hydromechanics (hi'dro-me-kan'iks), n. [< Gr. 
vSup (Mp-), water, + E. mechanics, q. v.] The 
science of the mechanics of fluids, or of their 
2937 
laws of equilibrium and motion, including the 
divisions of hydrostatics and hydrodynamics, 
and also hydraulics. 
It is perhaps superfluous to speak of the important place 
which the subject of hydromechanics has occupied in 
modern mathematical physics since the labors of Helm- 
holtz, Maxwell, and Thomson in reducing the mathe- 
matical treatment of electricity and magnetism to that of 
the motion of incompressible fluids. Science, III. 78. 
hydromedusa (hi'dro-me-du'sa), n.; pi. hydro- 
mcdus(K (-se). [NL. (cf. Gr. '"fopo/ieoovaa, the 
name of a frog in the poem " Batrachomyo- 
machia"), < Gr. vdup (l>dp-), water, + MeAovaa, 
Medusa: see Medina, medusa.'] 1. Same as 
lii/ilroinediisan. 
One hydromedusa lays its eggs early in the morning. 
Science, IV. 429. 
2. [cap.~] A genus of reptiles. Wagler. 
HydromedllSSB (hi"dro-me-du'se), n.pl. [NL., 
pi. of Hydromcdusa, q. v.] A zoological group, 
variously limited, (a) A class of coslenterates cor- 
responding to the class Hydrozoa. C. Vogt, 1861. (b) A 
subclass of Hydrozoa, contrasted with ScyphomeduHce, 
containing all those hydrozoans which are related to Hy- 
dra through the fact of reproducing by means of lateral 
gemmation, not by strobilation or scyphistoma. This sub- 
class is composed of the gymnoblastic and calyptoblastic 
hydroids, the trachymedusans and narcomedusans, the 
hydrocorallines, and the siphonophorans. The non-sexual 
individuals constitute the characteristic hydroids, of com- 
paratively narrow and elongate form, often branching or 
aggregated in colonies. In this sense the group corre- 
sponds to the cryptocarpons discophorans of Eschscholtz, 
the Craspedota of Gegenbaur, the Cycloneura of Eiiuer, 
and the Hydroida or Hydroidea of various authors. 
hydromedusan (hl"dro-me-du'san), a. and n. 
I. a. Of or pertaining to the Hydromedusce. 
II. . A member of the Hydromedusai. Also 
hydromedusa. 
Hydroniedusinse (hi-dro-me-du-si'ne), n.pl. 
[NL., < Hydromedusa + -i<E.] Same as Hy- 
dromedusa!. 
hydromedusoid (hi^dro-me-du'soid), a. [< 
Hydromedusa + -oid.~] Having the characters 
of the Hydromedusce; resembling the Hydro- 
medusa!. 
hydromel (hi'dro-mel), n. [< F. hydromel = 
Sp. hidromel = Pg. hydromel = It. idromeJe, < L. 
hydromel, hydromeli, < Gr. v6p6fie^.i, a kind of 
mead made of water and honey, < Map (Mp-), 
water, + peKi = L. mel, honey.] A liquor con- 
sisting of honey diluted with water, ferment- 
ed or unfermented: in the former case called 
vinous hydromel, and also mead. 
As touching the mead called Hydromell, it consisted in 
times past of rain water, well purified, and hony. 
Holland, tr. of Pliny, xxxi. 6. 
Hydromel, or watsr-hony, in long continuance will be- 
come wine. Hakluyt's Voyages, I. 566. 
In divers parts of Muscovy and some other northern 
regions, the common drink is hydromel, made of water 
fermented with honey ; and indeed, if a due proportion 
betwixt those two be observed, and the fermentation be 
skillfully ordered, there may be that way, as experience 
hath assured us, prepared such a liquor, both for clear- 
ness, strength, and wholesomeness, as few that have not 
tasted such a one would believe. 
Boyle, Usefulness of Nat. Philos., ii. 4. 
They [British Oauls] drank beer and hydromel, which 
was carried about in metal beakers or jugs of earthen- 
ware. C. Elton, Origins of Eng. Hist., p. 122. 
hydromeningitis (hi-dro-men-in-jl'tis), n. 
[NL., < Gr. voup (Mp-), water, + NL. meningitis, 
q. v.] In pathol., meningitis with serous effu- 
sion. See meningitis. 
hydrometallurgy (hi-dro-met'al-er-ji), . [< 
Gr. Map (Mp-), water, + metallurgy.'] The pro- 
cess of assaying or reducing ores by liquid re- 
agents. 
hydrometamorphism(hi-dro-met-a-m6r'fizm), 
n. [< Gr. iidop (Mp-), water, + E. meiamorphism.'] 
A kind of metamorphism of igneous rocks 
brought about by water, in contradistinction to 
pyrometamorphism, or metamorphism of sedi- 
mentary rocks effected by heat. 
hydrometeor (hi-dro-me'te-or), n. [< Gr. Mop 
(Mp-), water, + (NGr.) iitrsupov, a meteor: see 
meteor.'] A meteor or atmospheric phenome- 
non dependent upon the vapor of water ; in the 
plural, all the aqueous phenomena of the at- 
mosphere, as rain, hail, snow, etc. 
hydrometeorological (hi-dr6-me"te-or-o-loj'i- 
kal), a. [< hydrometeorology + -ic-al.^] Relating 
or pertaining to hydrometeorology. 
hydrometeorology (hi-dro-me"te-o-rol'o-ji), n. 
[< Gr. Map (Mp-), water, + uereupoXoyia, meteor- 
ology: see: meteorology. Cf. hydrometeor. ~\ That 
branch of meteorology which is concerned with 
water in the atmosphere in the form of rain, 
clouds, snow, hail, etc. 
hydrometer (lii-drom'e-ter),w. [<&T.v6pofiTpiov, 
a vessel for measuring hydrostatically, < Map 
(Mp-), water, + /ierpov, a measure.] 1 . An instru- 
Nichol&on's Hydrometer. 
Common Form of Hy- 
drometer for liquids, in hy- 
drometer-glass. 
hydromicaceous 
ment for measuring 
specific gravity, es- 
pecially that of water 
and other fluids, and 
hence the strength 
of spirituous liquors 
and of various solu- 
tions. In Nicholson's 
hydrometer for solids (see 
cut) the weight is first de- 
termined which, placed in 
theupperpan, willdepress 
the instrument to the zero- 
mark (a); then the weights 
are found which are need- 
ed to do this when the 
body experimented upon 
is placed, nrst in the upper 
and then in the lower pan. 
The difference between 
these last weights and 
that first found gives the 
weight of the body in air 
and in water respectively, 
whence the specific gravity is calculated in the usual man- 
ner. The common type of hydrometer for liquids consists 
of a glass tube with a graduated 
stem of uniform diameter, a bulb 
to cause it to float in the liquid, and 
a weight or counterpoise to cause 
the stem to stand upright as it 
floats. From the reading of the 
scale at the point which is on a 
level with the surface of the liquid 
in which it is floating, the specific 
gravity is ascertained either di- 
rectly or by a simple calculation. 
Scales in common use are those of 
Beaume, as applicable to liquids 
either more or less den&e than wa- 
ter ; in the former case the zero is 
near the top, and in the latter near 
the bottom of the stem ; the gradu- 
ation is conventional, and the spe- 
cific gravity is obtained from the 
reading by means of a series of ta- 
bles. AnotherfonnisthatofTwed- 
dell. Hydrometers constructed to 
measure the purity, density, orde- 
gree of concentration of particu- 
lar liquids receive special names, 
as alcoholometer, lactometer, etc. 
2. Air instrument used for 
measuring the velocity or discharge of water, 
as in rivers, from reservoirs, etc. 
Hydrometra 1 (hl-drom'e-tra), n. [NL., < Gr. 
Map (Mp-), water, + [ttTpov,"a, measure.] The 
typical genus of the family Hydrometridte. The 
European H. utagnorum and the American H. linearis are 
examples. The genus as originally established by Fabri- 
cius (1796) was divided by Latreille (1807) into Hydrometra 
proper, Gerria, and Velia. 
hydrometra 2 (hi-dro-me'tra), . [NL., < Gr. 
Map (Mp-), water, + ////rpa, uterus.] Inpathol., 
catarrhal endometritis. 
There sometimes exists a form of catarrhal inflamma- 
tion of the lining membrane of the uterus, giving rise to 
a mucous or muco-purulent secretion. ... If the fluid is 
wateiy, this is called hydrome-tra. 
R. Barnes, Dis. of Women, p. 180. 
hydrometric (hi-dro-met'rik), a. [As hydrome- 
ter + -ic.] 1. Pertaining to a hydrometer, or 
to the determination of the specific gravity, 
velocity, discharge, etc., of fluids. 2. Made by 
means of a hydrometer: as, hydrometric ob- 
servations Hydrometric pendulum, an instrument 
consisting of a hollow ball suspended from the center of 
a graduated quadrant, and held in a stream to mark by its 
deflection the velocity of the current ; a current-gage. 
hydrometrid (hl-drom'e-trid), n. An insect of 
the family Hydrometridw. 
Hydrometridse (hi-dro-met'ri-de), n.pl. [NL., 
< Hydrometra 1 + -idee.'] A family of heteropter- 
ous insects with long legs fitted for walking on 
the water, typified by the genus Hydrometra. 
The family formerly included the genus Hydrometra in a 
broad sense, but the genera Velia and Gerris are now re- 
moved to other families. Species of the restricted fam- 
ily are frequently observed on the surface of pools and 
streams, where they walk with the very slender body ele- 
vated upon their long legs, but do not swim in the water 
like the true water-bugs, Hydrocorisa?. Also called Hy- 
drometrides, Hydrometnna, and Uydrometritet. 
hydrometrograph (hl-dro-met'ro-graf), n. [< 
Gr. Map (Mp-), water, + ftfrpov, a measure, + 
ypa<j>tiv, write, record.] An instrument for de- 
termining and recording the quantity of water 
discharged from an orifice in a given time. 
hydrometry (h!-drom'e-tri), n. [As hydrome- 
ter + -y.] The art or operation of determin- 
ing by means of hydrometers the specific grav- 
ity, density, velocity, etc., of fluids. 
hydromica (hi-dro-mi'ka), n. [< Gr. Mop (Mp-), 
water, -I- NL. mica, q. v.] A variety of potash- 
mica which contains more water than ordinary 
muscovite, and is less elastic. See mien. 
hydromicaceous (hl"dr6-ml-ka'shius), a. [< hy- 
(Irnmicd + -aceoiis.~\ Of the nature of hydro- 
mica; containing hydromica. 
