Description

Signed “Abraham & Co. Liverpool (1851-1875), this simple surveying instrument exhibits some unusual features of the day.

Surmounted above a 10 x 4 cm. brass plinth (for plane table or field tripod-2 cm. threaded hole) are a large bubble level and telescope (sighting tube) in parallel, each being 23 x 2 cm. Above them is a 6 cm. diameter compass with paper dial divided into single degrees with a full 360 degree circle and cardinal points. Needle on brass pivot with ingeneous trip lever to lock or stop needle movement once the cap is applied (or by hand). The glass has an etched line running the full diameter which can be rotated to a maximum of 25 degrees to account for magnetic vs. geographic North. Focussing is acheived by draw tube and threaded eyepiece (fine optics) and the cross hairs are found internally in the body tube (not in the lenses). Original patination of the instrument from handling over the years but you can see the brilliant lacquering on the inner surface of the compass protective cap and plinth (see photos). I have never seen another example of this unusual arrangement in a simple surveying instrument. Intact and original.