Page:Dictionary of aviation.djvu/186

 162 DICTIONARY OF AVIATION

obscuration ,bskc.u'zee-$an n. the act of obscuring or dark- ening; the state of being obscured: as, the obscuration of the moon in an eclipse; specifically, in meteorology, the darkening or hiding of the sun by clouds; cloudiness.

observation-kite ,ebz9^'vee-S9n / kait. a man^hfting kite used in warfare for purposes of observation or reconnais- sance; a war^kite.

observer ab'zeiz-vaz n. a soldier or other person whose busi- ness is to observ the enemy from an airship; one who makes a reconnaissance iuhile riding in a balloon or aero- plane.

observing-board 9b'zB:z-vin,bo:zd n. a board or board^like structure sometimes used in balloons in connection with the making of observations.

observing-station 9b'zB:z-virj,stee-$9n n. a station uuhere meteorological observations are made; a wether^station,

obstacle 'ebsta-ka! n. any hindrance or obstruction to the motion of air or other fluid, as an aerofoil.

ocellus o'setes n. one of the eye^like spots in the taiMethers of a peacock or in the wing of an argus^f esant ; an eye^spet.

oil-silk '0il,si}k n. silk cloth impregnated with boild eil, semitjansparent, waterproof, and gasproof, used in making balloon^envelops or gasbags; eild silk.

oilskin 'oilskin n. cloth made gasproof or waterproof by treatment with oil, often used in making balloons and other aircraft; cotton, silk, or linen fabric prepared with oil so as to be impermeable.

one-man 'wAn,m3en adj. perfermd by one man only : as, a
 * one?man exhibition flight.

operating-wire 'p9-zetirj,waiz n. a wire, in a flymg^ma- chine, used in operating the rudder; a rudder^eperating wire.

orbit ':z-bit n. a tr,ack, course, or circuit; a circular or ellip- tical path; the rbitelike oval flightepath of a bird soaring against the wind : as, the form of *orbit in dynamic soaring.

Ferrel's orbit theory, a theory advanced by Ferrel attpb- uting the growth of hailstones to their motion in loop^like orbits or paths in and out of the air^stjata where rain or ice is forming.

orbital ':z-bi-tl adj. taking place in an orbit; of revolution.

orbit-motion 'erz-bi^moo-fen n. motion in an erbit; move- ment along a path, as a circle or ellipse, which returns upon itself.

ornitnopter ^zni'Oeptaz n. [also spelt ornithopt&re] a bird^ wing flying^machine ; a hevier^than^air aerial vehicle de- signed to fly by means of flapping or oscillating wings,

�� �