抄録
Among many ways of projecting a spherical figure on a plane surface at equal angles, the simplest one is the stereographic projection. By utilizing this projection, a spherical circle is directly projected as a circle on a plane surface and specifically the great circles passing through the projecting point are projected as straight lines, and there are no angular distortions between the spherical figures and the plane figures thus projected. By availing these characteristics, the spherical constructions can be made on a plane surface, and thus, we endeavoured to find a simple way of solving the astronomical triangles by means of the geometrical construction using rulers and a drawing compass in a short time instead of doing the complicated navigational calculations hitherto applied. As the result we have now obtained a successful plan with regard to the azimuth diagram. (refer to Fig.2 on this paper)
