116 DICTIONARY OF AVIATION
electric gradient, the gradient of the electric potential of the atmosfere; the vertical or the horizontal rate of change in the potential function of the electricity in the air.
gradient of refraction, the vertical temperature-gradient at considerable altitudes as affected by fenemena of re- fraction.
initial gradient, the small gradient of pressure of the air at about sea-level tuhere the slight variations of pressure due to differences of density of the air, the tides, etc., initiate or give rise to the winds which cause the larger (observd) barometric gradients.
neutral gradient of pressure, a vertical pressure-gradient whose maintainance keeps the atmosfere neutral or in dy- namic equilibrium.
vertical gradient, the gradient according to vertical height above the earth; the rate at tuhich any atmosferic condition, as temperature or pressure, etc., varies with the altitude. gradient-formula 'gzee-di-3nt,fe:z-mjo-l3 n.
Ferrel's gradient ^formula, a formula expressing the re- lation between barometric gradient and the accompanying winds.
grading 'gzee-dirj n. the mode in which a propeller-blade or other aerofoil is graded or graduated in outline, contour, or curvature of surface for a definit purpose; the form of curvature or contour which results from this process : as, segmental *grading.
linear grading, the grading of a propeller-blade along the line of its radius. This grading, for any given radius, is the quotient obtaind by dividing the load-value by the thrust-value.
load grading, the grading of a propeller-blade in corre- lation with the distribution of its load.
thrust grading, the grading of the propeller-blade in cor- relation with the distribution of its thrust. grapnel 'gzaepNal n. a small anchor with three or more flukes, carried in a balloon and used for securing the bal- loon to earth en its descent; a grappling-iron; a grapple* iron ; an anchor.
grapple-hook 'gzsep^hok n. a grapnel; a grappling-iron. grapple-iron 'geaepa^ai-szn n. a grapple-hook; a grappling- iron; a grapnel. grapple-rope 'gzaepa^zoop n. the rope to mhich a grapple is
attacht to a balloon; an anchor-rope. grappling 'gzaeptirj n. a grappling-iron; a grapnel. grappling-iron 'gzsep^ir^ai-azn n. a device made of iron
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