Note 139 — Chapter XXXI · SPITSBERGEN EXPEDITIONS BEFORE 1872
Reading edition
The instrument consists of four arcs graduated so as to read to 30 with the verniers. Two of these arcs, representing the altitude and latitude, are moveable. The two others, which represent the declination and hour circle, are fixed. In using it the verniers of the proper arcs are set to the declination, the altitude, and the latitude respectively. The readings on the hour circle will then show the hour angle.