16-inch Hadley’s Quadrant (octant) – around 1740, England or North America
Stock Number: NM.4-45
The first octant was created by John Headly in 1731. In Great Britain and North America it was called the Hadley’s quadrant to distinguish it from the Davis Quadrant. The early octants of Hadley are provided with a transversal nonius, like the Davis Quadrant. Headly got a patent for eleven years in 1734. Immediately after it came to an end other instrumentmakers started with making octants. They are all equipped with a Vernier nonius, invented by the Frenchman Vernier.
1730 - 1745
Countries of manufacture
UK and Ireland, North America
This instrument is made of very fine Cuba mahogany and dates around 1734 -1745. Octants like this one with transversal nonius are mostly from John Headley. The transversal scale is made of palm wood. The scale can be read very accurately by means of an ivory insert in the alhidade. In the graduation every degree is divided in parts of 20 minutes. The nonius is divided in ten equal parts, so the accuracy of reading with the transversal nonius is two minutes. Remarkable detail: the vernier has a scale for backward observations, but no third mirror that makes that possible. On the left leg for a number of days probably the height values of a star (Afnil?) are displayed in pencil. The nameplate is made of ivory. The instrument does not have feet at the backside. Movable sunshades can easily fall overboard or get lost. Here they are missing.
The chest is largely made of cedar wood. The standing edge at the front was restored once. A compass rose is drawn in pencil in the lid with the initials G.M. and the year 1790.
Date: appr. 1730-1745
HWL case: 9,2x42x47 cm
HW instrument: 46×38 cm
Radius (rotation axis till nonius): 38.2 cm
Signed in case: G.M. 1790 in a compass rose and Capt. Monro with chalk
Origin: England or North America, possibly made by John Headley
Condition: very good for its age with some general signs of use and wear
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Welcome to the catalogue of Archipel International Maritime Gallery, specialist in nautical antiques and collectables.
Archipel International Maritime Galery in the Netherlands, sets itself to maritime objects, globes and sea charts of before 1900. The managing director worked as officer with the mercantile marine and the Royal Navy. As curator he was connected to one of the University Museums in the Netherlands. As seaman and curator he has a lot of knowledge of naval history. The entire Archipel collection can be found at the site Archipel-img.com.