Air navigation has so far been only by dead reckoning; with long distance flights overseas such methods are no longer adequate.—Methods of position fixing by astronomical observations.—Difficulties of taking sights in the air.— Visibility of the horizon.—Cloud horizons.—“Dip.”—The Baker Air Sextant.— Gravity controlled vertical for sight taking.

Difficulties of working out the observations in the air.—The navigation machine.—Curves of constant altitude and constant position angle.—The equations of their mercator projections.—The radii of curvature.—Error of declination treated as a correction to altitude.—Special slide rule.—Star curves.—Chronometers for air work.—Practical construction of altitude and position angle curves.—Checks upon the accuracy.

Run between sights.—Theoretical case.