Page:Dictionary of aviation.djvu/114

 90 DICTIONARY OF AVIATION

whenever moved slightly from its position, will remain in its new position; the equilibrium of a directionally bal- anced aerodone; indifferent equilibrium.

stable equilibrium, equilibrium in which the bedy con- cernd, whenever slightly moved out of its position, tends to return to its posiion.

unstable equilibrium, equilibrium in tuhich the bedy concernd, whenever slightly moved out of its position, tends to depart from it still further.

vertical equilibrium, the state of equilibrium or balance of an airship whose flight is being maintaind at the equi- libriunudevel, there being no advantage in changing its altitude or vertical distance from the earth.

equilibrium-level ,ikioi'hbd-3m'lev3l n. the level or hori- zontal plane of equilibrium or balance, for any given air- ship, so far as concerns its speed or economies of travel; the level of optimum altitude for an aeroplane or other air- ship, at tuhich it is in vertical equilibrium, or cannot easily rise higher or advantageously sink lower.

equilibrize i ktuili,bzaiz tr. [also spelt equilibrise'} equili- brate; balance.

equinoctial ^kiui'nokSgl adj. pertaining to a state of equal day and night; also, pertaining to the period or point of the equinox : as, an *equinectial storm.

escape-valve Xskeep/vselv n. [also spelt escapetvalv] the valv in the envelop of a balloon by which gas is allowd to escape from the bag, thus causing the craft to descend; a balloon^valv ; a safety^valv.

ether 'ii-03z n. [also spelt aether]

1. the upper air; the blue hevens.

2. a hypothetic medium possessing great elasticity to- gether with other qualities of a somewhat paradoxical na- ture, supposed to be diffused thruout space, to pervade all material bodies, and to serv to transmit light, heat, and other forms of radiant motion.

ethereal I'Oir-zi-al adj. [also spelt etherial and, formerly, aethereal]

1. fermd of, containing, or fild.with the ether or air of the upper regions; of or pertaining to the hevens; hevenly; celestial : as, *ethereal space, *ethereal regions.

2. of or pertaining to the ether of space : as, the *ethereal medium.

euplexoptera ,juptek'sopt3-za n. pi. a suborder of erthop- terous insects identical with the order Dermaptera, having the under wings folded crosswise and lengthwise; the ear- wigs or Ferficulidae; the Eupleceptera.

�� �