A good Barker’s Patent Abney’s Level with Prismatic Compass in Original Case by Francis Barker & Son for C.F. Casella & Co c1910

Abney level having 2⅜” diameter brass protractor with a range 90°-0°-90° attached to a spirit level with adjustment wheel. The whole mounted on a 4½” long square brass tube containing a mirror and a telescopic sight. 1½” diameter hand-drawn green card Singer style compass on jewelled suspension affixed to top with prismatic and wire sights, momentary brake, wire sight-activated transit lock. Marked by the retailer, “C.F. Casella & Co, London” and contained in its original leather covered, silk and velvet lined travel case, twin swinging catches.

Condition: In very good antique condition overall, all parts moving smoothly, the compass card clean and flat, the prism with partial hazing, the travel case covering with some losses, the silk and velvet linings faded.

Comments: The Abney clinometer and level, invented by Sir William de Wiveleslie Abney whilst associated with the The School of Military engineering at Chatham, is typically used at the eye height of the surveyor, either hand-held or mounted on a staff at that height. To measure lines on a particular slope, the desired angle or grade is first set on the level and then the surveyor sights through the sighting tube and brings the cross-hair in line with the bubble in the level while viewing the target. This allows the surveyor to see if the target is above or below the line of sight.

To measure an unknown slope, the surveyor first sights a target along that slope and then adjusts the angle of the level until the bubble is centred on the cross-hair. Once this is done, the slope may be read from the scale.

This Abney’s Level dates to the early 1900s and is marked “C.F. Casella.” It featured in Barker’s catalogue of 1909, see image, the same year as Barker’s patent application, and will be supplied with a copy of the original instruction sheet (NB: the image of the original instructions is for information only).

A rare and interesting instrument, and one for the collector.