What is "spherograph"

Spherograph \Spher"o*graph\, n. [Sphere + -graph.] An instrument for facilitating the practical use of spherics in navigation and astronomy, being constructed of two cardboards containing various circles, and turning upon each other in such a manner that any possible spherical triangle may be readily found, and the measures of the parts read off by inspection.

n. An instrument for facilitating the practical use of spherics in navigation and astronomy, constructed of two cardboards containing various circles, turning upon each other in such a manner that any possible spherical triangle may be readily found, and the measures of the parts read off.