The Museum’s most recent acquisition is a folding gunner’s rule from the late seventeenth century. It consists of two 9-imch wooden arms connected by a brass hinge, and a thin brass arm pivoting at one end: this can be set at 90 degrees to the wooden arms to allow a plumb-line to hand from its tip and fall across a degree scale.
In different configurations the rule can act as a vertical instrument for taking altitudes or as a clinometer for a cannon. A variety of scales permit calculations connecting range, inclination, weight of shot and powder, and so on.
Since many artillery instruments seem impossibly fine and too complex for actual use, it is pleasing to acquire what appears to be a useful working tool. It is also gratifying to have an otherwise unrecorded signature and a date: ‘Bengiman Jobson 1680’.
Although early wooden instruments are now much less common than brass ones, there is no reason to believe this was the case in the period of their manufacture and use: brass instruments survive better and have always, justifiably or not, been more highly prized.