Dividers (or “compasses”) were needed to measure off distances on both Sectors and later the Gunter Scale (prior to the development of the slide rule). They were also used by astronomers, architects, engineers1, and navigators to measure off distances on plans and charts, and by skilled artisans to measure off distances on work.
These dividers are of English design seen normally in the period between 1740 and 1810 (this being only a rough dating based on similarities with others from the period), the lower pair being more typical of the earlier part of the period, and the upper (shorter pair) being more typical of the later part of the period. Unlike later dividers, with these the pointed steel legs are dovetailed into the brass upper arms of the instruments.
Each of these instruments has the usual overall shape for the period including a recess to enable the two legs to be easily pulled apart.
Each of these instruments has an extended inner flange under the head joint to ensure there is adequate friction thus holding the legs at the set angle. The older (longer) pair (~1750) is held at the head joint by a quite solid brass pin flanged at each end and ground flat. The more recent pair (~1800) is held by a metal pin (also flanged at each end, but probably of similar metal to the pointed steel legs) and has a more elaborate head joint. Neither has the later generation of head joint which was capable of being tightened using a threaded flat washer with two holes which, with the aid of a corresponding tool with two prongs, could be screwed down on a thread on the end of the axle pin. On the other hand, both have retained commendable tightness after more that two centuries.
1 According to the Oxford English Dictionary in early use ‘engineer’ or formerly ‘ingineer’ referred to a designer of fortifications and weapons (↑)
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