Oi. 



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H YL 



or that property of liquids by which they 

 transmit pressure equally in every direc- 

 tion. 



36. Hydro-static paradox. A term de- 

 noting that any quantity of fluid, how- 

 ever small, may be made to balance or 

 counterpoise any quantity, however large. 



37. Hydro-sulphuret. A compound of 

 sulphuretted hydrogen with a salifiable 

 base. 



38. Hydro-thionic acid {Oeiov, sulphur). 

 A name given in Germany to sul- 

 phuretted hydrogen, or the hydro-sul- 

 phuric acid of Gay Lussac. 



39. Hydro-zoa (vipa, hydra, and ^Cbov, 

 an animal). Hydriform Polyps ; a term 

 applied by Owen to a class of Polyps, 

 which are organized like the hydra, or 

 common fresh-water polype. These cor- 

 respond with the Dimorphcea of Ehren- 

 berg, the Serlulariens of Milne Edwards, 

 and the Nudibrachiata of Farre. 



40. Hydr-uret, or Hydroguret, A com- 

 pound of hydrogen with a metal. 



41. Hydrus. The Water Snake ; a 

 modern southern constellation, consist- 

 ing of ten stars. 



HYGRO'METER. (i/TPo?, moist, )ue- 

 Tpov, a measure). An instrument for 

 ascertaining the degree of moisture of 

 the atmosphere. The quantity of 

 moisture present in the air is inferred 

 from the reduction of temperature re- 

 quired to produce a deposition of dew 

 from the air ; the less the reduction of 

 temperature required, the greater the 

 amount of moisture in the air. 



Hygrometric Water. That portion of 

 moisture which gases yield to deliques- 

 cent salts. 



HY'GROSCOPE (u7po9, moist, (tko- 

 nea, to examine). An instrument for 

 indicating the presence of aqueous va- 

 pour in the atmosphere, without mea- 

 suring the amount. Hygroscopic sub- 

 stances are mostly of animal or vegetable 

 origin, as hair, fish-bone, animal mem- 

 branes, the beard of the wild oat, &c. 



HYLtE'OSAURUS ({/Aalov, of the 

 wood, aavpo^, a lizard). An extinct gi- 

 gantic land reptile, of the Wealden strata 

 of Kent and Sussex, forming, with the 

 megalosaurus and iguanodon, a natu- 

 ral and well-marked group of colossal 

 animals, connected with the middle se- 

 condary period. 



HYLO'BATES (uXo/Sdrn?, one who 

 haunts the wood). The name given by 

 Illiger to the long-armed Apes or Gib- 

 bons, which haunt the forests, and re- 

 semble the Orangs in form and dentition. 

 171 



HYP 



HYME'NIUM {vfirjv, a membrane). 

 That part of a fungaceous plant in which 

 the sporules immediately lie : in agaricus 

 it consists of parallel plates, called la- 

 mellcB, or gills. 



HYMENO'PTERA {Ifx^v, a mem- 

 brane, TTTepov, a wing). An order of 

 mandibulate insects, which have four 

 membranous, naked, and unequal wings, 

 and undergo complete metamorphosis, as 

 the wasp. They are distinguished by 

 Latreille into the terebrantia, in which 

 the abdomen of the females is furnished 

 with a saw or borer ; and the aculeata, 

 in which the abdomen of the females is 

 armed with a sting. 



HYPER (i/Trep, over or above). A 

 Greek preposition, denoting a position 

 above, or excess. In chemical nomen- 

 clature, it denotes that the acids to which 

 it is prefixed contain more oxygen than 

 those to which the word per is prefixed, 

 as hyper-chloric acid. It corresponds 

 with the Latin preposition super. 



HYPE'RBOLA {iTrep/SoXij, a throwing 

 beyond). A section of a cone by a plane, 

 which, if extended, would cut the oppo- 

 site cone, so that the sections of both 

 cones will exhibit curves expanding 

 continually, like the parabola, but with 

 different properties. This conic section 

 is called a hyperbola, because the angle 

 which its plane forms with the base of the 

 cone is greater than that of the parabola. 

 Hyperbol-oid (et'^oc, likeness). A geo- 

 metrical solid, formed by the motion of a 

 hyperbola round its axis. It is also 

 termed a hyperbolic conoid. 



HY'PERSTHENE. Labrador horn- 

 blende. A variety of augite, of a green- 

 ish-black colour, very similar in its 

 general appearances and characters to 

 diallage. It consists of silica, oxide of 

 iron, magnesia, and alumina. 



Hypersthene Rock. A compound of 

 hypersthene and felspar, the latter being 

 compact, crystalline, or glassy. These 

 form three varieties, to which M'Cul- 

 lock has given the general name of 

 hypersthene rock. 



HYPHA (v<pt], a web). A term applied 

 by Willdenow to the filamentous, fleshy, 

 waterjf thallus of byssaceae. 



HYP-, HYPO- ({/TTo, under). A Greek 

 preposition, signifying a position under, 

 or deficiency. In chemical nomenclature 

 it denotes the presence of a smaller 

 quantity of acid than is found in the 

 compounds to which it is prefixed. It 

 corresponds, in all these applications, to 

 the Latin preposition sub : — 

 12 



