Large 18th Century, 20 inch Octant, mahogany
An early and interesting two mirror octant with Vernier nonius.
The first octant was created by Headly in 1731. In Great-Britain and North-America the instrument was called the Hadley’s quadrant to distinguish it from the Davis quadrant. Headly got in 1734 a patent for eleven years. Immediately after it came to an end other instrumentmakers started with making octants.
This octant is an early mahogany one. The graduated scale reds from -5 to 95 degrees and is made of ivory with a Vernier nonius. The engraving of the scale is made by hand. At the graduation every degree is divided in parts of 20 minutes. The Vernier nonius is divided in twenty equal parts. The accuracy of reading with this nonius is one minute.
The peepsight has one hole. Floral motifs are engraved by hand on the alhidade. Although the instrument only has a horizontal mirror, the sunshades are still removable.
This beautiful instrument has a nice patin. On the backside three brass legs and the adjusting-screw fort he horizon mirror. The mirror table of this octant is also made of brass.
Date: 1780 – 1800
HW: 51,5×41 cm (20×16 in)
Radius (rotation axis till nonius): 44 cm (17.2 in)
Signed: not signed
Condition: very well