190 DICTIONARY OF AVIATION
��rudder-lever 'zActo^hi-vaz n. a lever in an airship, used to
control a rudder. rudder-plane 'zAdgz^pteen n. an aeroplane used in or as a
rudder, as in a Zeppelin airship; a steenng^plane. rudder-rope 'zAda^zoop n. the rope by tuhich the steersman
or aeronaut controls the rudder of an airship. rudder- tail 'zAdaz^teel n. a tail acting as a rudder; an air-
ship^tail designed to function as a rudder; a steenng^tail. rudder-wheel 'eAdaz,iuiil n. a wheel by which the rudder of
an airship is contjold; a steermg^iuheel. rule zuul n. the expression of a uniformity among fenemena;
a minor law; a formula.
Archibald's rule, the rule stated by E. D. Archibald as to
the rate of diminution of wind^velecity with altitude. Broun' s rule, the rule stated by J. Allan Broun, in 1845,
as to the direction of the movement of lower cumulus scud,
etc.
Buchan's rule, the rule formulated by A. Buchan, in 1865,
as fellows : "Stand with your left hand toward the center of
low barometer and your right hand toward the high, then,
in the northern hemisfere, the wind will be en your
back."
Espy's rule, the rough rule stated by Espy, about 1834,
that the altitude (in feet), above the observer, of the base of
cumulus cloud is 300 times the depression of the dew-point
(in Fahrenheit degrees) at the locality of the observer. Gallon's anticyclonic rule, see under anticyclonic. Meldrum's rules, the rules formulated by C. Meldrum for
guidance in hurricanes in the Indian Ocean. These rules
were elaborated by Blanford, in 1888.
Stevenson's rule, a rule or formula stated by Stevenson
as to the velocity of wind, over level land^surfaces in-
creasing with the altitude. run zAn n. the buttock and tail (taken together) of an aero-
foil or other streamline body; the stern or afterbody of an
airship of streamline form : as, the flow has net time to
close in round the *run : distinguisht from entrance. runner 'zAnaz n. a skid, skate, or the like, attacht under a
flying^machine so as to allow it to run or slide along upon
the ground in alighting; a landing^skid. running-gear 'zAnin,gi:z n the gear or apparatus by
which a flying^machine is run or operated; the underbedy
or chassis. running-rope 'zAnirj,zoop n. a fastening^rope, as in an air-
ship or flyer, tuhich, as it is loosend or let go and allowd
to run out, permits the craft to rise.
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