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 DICTIONARY OF AVIATION 89

positions at different seasons of the year, etc., and pass- ing thru the points of maximum temperature; the line along tuhich the greatest heat occurs at the earth's sur- face.

3. an imaginary great circle of the gasbag of an inflated sferical balloon, whose plane is perpendicular to the ver- tical axis of the balloon. equatorial ,ikiu9'to:-n-9l adj. pertaining to the equator of

the gasbag of a balloon. equilibrate ,iku)i'lai,bzet tr. bring into or keep in a state of

equilibrium or equipoise; equilibrize; balance. equilibration ,ikiuiJi'bzee-$9n n. the action or process of bringing into or keeping in equilibrium or equipeise; the state or condition of being balanced.

equilibrator ,ikuui'lai,bzet9z n. a long rope-like device at- tacht to a dirigible balloon and capable of being lowerd and raised in order to equilibrate or stedy the craft or keep it at a certain constant height, as from the surface of the sea below; a balancer; a guide-rope.

equilibrium ,iktui'hbzi-3tn n. [ploral equilibria] the state or condition of equipoise; the state of a material system in tuhich the forces acting on the system are evenly bal- anced, or such that their resultant is zero; the state of an airship luhen the resultant of all the air-pressures upon it is vertical and passes thru the center of gravity of the craft; balance.

atmospheric equilibrium, the state of equilibrium or bal- ance among the various parts of the atmosfere, as related to horizontal or vertical movements of the air, etc.

automatic equilibrium, same meaning as automatic bal- ance, see under balance (noun).

equilibrium of direction, equilibrium or stediness in the general direction of the course or flight-path of an aero- done, such as is provided by a directiv fin or wind-vane, and identical in kind to that which is afforded an arrow by its f ether; directional equilibrium, balance, or stability, compare dir ectiont maintenance.

lateral equilibrium, same meaning as lateral stability. see under stability.

longitudinal equilibrium, same meaning as longitudinal stability, see under stability.

moving equilibrium, equilibrium in which the bedy con- cernd is in motion; the condition of having equilibrated or balanced movement.

neutral equilibrium, equilibrium in which the bedy con- cernd is neutjal or indifferent as to its exact position, er,

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