Brass Sector (A#1467)
Developed in the late 16th century, sectors are hinged measuring instruments with graduated legs. They were capable of performing a wide range of calculations—some having as many as twenty or more different mathematical functions.
While sectors were most often used at sea for navigation, A#1467 was intended primarily for use in gunnery to calculate ballistics and trajectory.
Of French manufacture, the inscriptions on its surface are Les Cordes (“the chords”), Le partes Egaltes (“the equal parts”), Les Solides (“the solids”), Les Metaux (“the metals”), Les Plans (“the Planes), and poids des boulets (“weight of cannonballs”).
On matching sides of the ventral faces of the sector are increments marked off on an angled scale from 0 to 200.
The dorsal side of the sector has a set of angled scales that range from 0 to 160 on opposing arms of the scale. Another scale on this face is less sharply angled and ranges from approximately 0 to 60 (some of the lettering is worn). The final scale runs parallel with the edge of the legs of the sector and appears to range from 0 to 90 (the last sets of increments of the scales being abraded).
The various sets of measured scales appear to be arranged so that relationships based on degree measurements can be determined by lining up the figures of the scales against the desired angles; in order to, for example, determine the necessary elevation of a cannon to achieve a desired range for different sized shot.
It is believed that a veteran French gunner named Taffier was a member of Bellamy’s crew who might have used this instrument.
