Description

Octagonal surveyor’s cross (or équerre) in brass (c. 1900). Possibly French. Wood and paper cylindrical box (severely damaged).

The octagonal form of a surveyor’s cross is also known as a French cross-staff. It comes in two parts (see image 3): (1) the main body of the device and (2) a separate handle or base. When in use the base is screwed into the main body to allow it to be handled and it also has socket so that it can be fitted on to a pointed staff (see images 1 and 2). When not in use the base can be inserted into the top of the device and secured for storage in the box (see image 4).

The box has “Morgan [?] Gordon 24-11-00” written in ink suggesting the date 24 November 1900 (see image 5). Inside the lid of the box is the text “6/8/-” perhaps suggesting purchase price of 6 pounds 8 shillings (see image 6). Also inside the lid is the text “Staff 24” suggesting its use with staff number 24 (see image 7).

This device is used to set out angles in multiples of 45° and being octagonal is divided into 8 faces and hence 8 directions with corresponding sets of visors. There are two sets of slits: those with (2 No) and those without a vertical hair (2 No). The ones without hair are narrow slits, each just under 1 mm wide. The remaining slits are narrow for one half, while the other half is wider at 5 mm wide, and contains the hair. Opposite sides of the instrument always have the same type of visors, but in the case of the ones with hair the opposite visors are inverted. The narrow slit opposite the wider one with the hair helps to get the hair into focus.

The surveyor’s cross and its use are built on the principles of the Roman groma.