Combined Altitude and Prismatic Compass by Francis Barker
This instrument combines both a prismatic compass and altitude reading instrument.
The Francis Barker Trade mark is present and it bears Patent No 1926 Serial Number 1340.
Acknowledgement to Compassipedia : provides information that Francis Barker filed a Patent on May 4th, 1881 for an improved prismatic compass with clinometer.
The Patent details together with a copy of a 1919 Trade Catalogue are shown in the pictures below.
Acknowledgement to Mathsinstruments :
When used as a clinometer the weighted clinometer card is released by pulling the knob at the top. Held vertically it is sighted in the same way as when used as a compass and the clinometer card read through the prism, which can be raised to suit. It can also be used to measure the slope of a surface by direct reading through the lower glass. There is a tripod or staff screw under the base plate for when it is used as a compass.
The leather case shows the inscription " 177 Coy RE ".
A book has been written by Iain McHenry about the 177 Company of Royal Engineers
"Subterranean sappers : a history of 177 Tunnelling Company RE from 1915 to 1919"