Leon McKinnon, age 14, of Davenport, Iowa, for his question:

WHO INVENTED THE SEXTANT?

A sextant is an instrument that measures the angular distance between any two points, such as the sun and the horizon. Navigators use it to find the position of their ships or aircraft. The mirror sextant was invented independently in 1730 by John Hadley in England and Thomas Godfrey in America.

The frame of a sextant supports the graduated arc of a sixth part of a circle, a movable arm which represents the radius of the circle, two mirrors and a small telescope.

One of the mirrors, the "horizon glass," is fixed. The second mirror, the "index glass," is screwed to the movable arm, or index bar. The telescope sharpens the line of the horizon.

The sextant is held so that the arc is vertical and the horizon shows in the horizon glass. The operator looks through the telescope at the horizon glass. Then he moves the index arm until the image of the sun or a certain star, reflected in the index glass, touches the horizon line.

The altitude of sun or star may be read from the graduated arc. The operator then compares this altitude at various degrees of latitude. Thus he finds the latitude of his ship or airplane.