DICTIONARY OF AVIATION 129
hydrodynamics ,hai-dro-dai'n3emiks adj. the science of the forces acting upen or exerted by liquids, now eften includ- ing both hydrostatics and hydrokinetics. see dynamic.
hydrogen 'hai-dra-dsm n. an elementary substance, under ordinary conditions a colorless, odorless gas, burning with a pale-green flame, and the lightest substance known, having a specific gravity of about one fourteenth that of air; used for inflating balloons; hydrogen gas.
liquid hydrogen, hydrogen in the liquid ferm; a colorless liquid obtaind by cooling hydrogen gas under great pres- sure.
hydrogen-balloon 'hai-dra-dsin-ba/loun n. a balloon whose gasbag is inflated with hydrogen gas.
hydrographic ,hai-dr3'gzaefik adj. [also spelt hydrografic] pertaining or relating to hydrografy.
hydrography ,hai'dregz9-fi n. [also spelt hydrografy'} the science or description of the seas, lakes, rivers, and other waters of the earth's surface as to distribution, contour, currents, shallows, and otherwise; the study and mapping of the water-features of the earth.
hydrometeor Jiai-drQ'mii-ti-az n. a meteor or atmosfenc fenemenon dependent upon water^vapor ; any one of the aqueous fenemena of the air, as cloud, rain, snow, hail.
hydrometeorological hai-d^miti-az^'ledsi-kal adj. of hydrometeorology.
hydrometeorology hai-dr9,miti-3'zelo-d3i n. that branch of meteorology which is concernd with hydrometeors.
hydroplane 'hai-dr3,pi,een .
1. a machine consisting essentially of a plane or plate designed to be driven by power aleng the surface of a body of water; a boat designed to ride en planes submerged in or skimming along the surface of water.
2. a plane or plate designed to be attacht to the lower part of an aeroplane flying-machine so as to enable the aeroplane to skim along on the surface of the sea or other body of water; a hydroplane plate attacht to a flying-ma- chine.
hydrostatic ,hai-dr3'stsetik adj.
1. relating to the equilibrium of, and pressure exerted by, liquids, when static or at rest; belonging to hydro- statics; also, depending on air-pressure.
2. floating in or en the water, as certain univalv shells; also, relating or instrumental thereto.
hygrodeik 'hai-gz3,daik n. -an instrument for showing the moisture or humidity of the air; a ferm of hygrometer con-
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