Surveyor's Vernier Compass
Diameter 5.5 inches; length 15 inches
This is an unusual instrument. The outer edge of the face is graduated to 10 degrees, and numbered from north and south. The rim is graduated to single degrees, numbered counter clockwise from north, and read by vernier to 6 minutes. Unlike most vernier compasses, however, this one has no variation arc. And unlike most surveyor's compasses, here the sight vanes are attached to the arms, and the arms screw onto the compass box. There is also a level vial mounted below the compass box, and a socket so that the compass can be used with a jacob staff. This instrument dates from the first half of the 19th century, when Robert Brettell Bate was working in London.