AbstractAperfected sextantwith artificial horizon for air navigation does not seem to have existed before the 1940's. Yet the history of attempts at developing an artificial horizon for celestial navigation can be traced back more than two centuries. In this study some of the early 18th century attempts to modify the old Davis quadrant and the new Hadley quadrant are described. Henry Serson's “whirling speculum”, apparently the first successful vertical gyro is discussed in some detail. Lastly, the age of air navigation is introduced by means of a study of the Willson, the Pioneer MK III, and the Kollsman pendulous mirror and bubble sextants. Note is made of parallel efforts in Portugal and Great Britain during the same per