Signed: Elias Allen fecit
As well as describing his 'circles of proportion', William Oughtred's text specified another instrument to be engraved on the reverse of the plate: the 'horizontal instrument', which is based on a projection of the celestial sphere. This example by Elias Allen, the leading English instrument maker of his day and a close collaborator of Oughtred, has both the 'circles of proportion' and the 'horizontal instrument'. The circles are in the revised form that was published in 1633 (catalogue no. 78), with the inclusion of two extra circles described in an additional section on navigation. Rather than a nocturnal as shown in the printed version of the instrument, there is a planispheric projection of the celestial sphere of the Rojas type inside the innermost circle.
This example of the instrument came almost directly to Oxford after being made: it was given to St John's College by George Barkham and an inscription records the date as 1635. Below the inscription Barkham's arms are prominently engraved. Not only does this provenance demonstrate the academic context of this particular example, but its large size strongly suggests that it would have served primarily for study and practice rather than for more active exertions.
Radius: 230 mm
St John's College Collection
Inventory no. 40,847