Description

REMARKABLE IN-LINE DOUBLE-REFLECTING MINIATURE QUINTANT, English, c. 1830, beautifully signed “Thomas Jones, 62 Charing Cross, London,” and stamped twice on the case “Hudson & Son, Greenwich.” This diminutive sextant is constructed of clear lacquered and chemically darkened brass, 4-1/4″ (11 cm) overall with a scale radius of just under 3″. It is shaped as a quarter-circle, with scale useable from -5° to 148° (and thus covering the 2 x 72° = 144° necessary for a quintant). The rotating index arm carries vernier reading to one-tenth degree, clamp-screw, and quite large mirror silvered but for a clear glass rectangular window within. To one side is a slit sighting vane, to the other a half-silvered “horizon” mirror. The frame is fitted with three legs and a hinged brass handle (which is pierced, probably to save weight). Condition is very fine with its fitted wood case. 

In use one sees straight ahead through the unsilvered portions of the two mirrors, and sees simultaneously the doubly-reflected image of the target. It is an ingenious layout, “surprisingly easy to use and makes a very good visual presentation of the sight” (p. 131 in Taking the Stars by Ifland, who illustrates a similar but unsigned example). It can be compared with the extraordinary in-line instrument of Amado Laguna (Tesseract Catalogue 101 Item 22) and with the equally ingenious (and rare) single mirror altitude quadrant of Thomas Jones (94/22). 

This well-known maker, who advertised as “Pupil of Ramsden,” had the present address from 1816 to 1850. The later retailer Hudson & Son is recorded in Greenwich in the late 19th century.