PRESENTED is a last half of the 18th C. mariner’s octant with
the mark of Jesse Ramsden on the arc. It was Ramsden who invented the dividing machine which allowed for the precision marking
of degrees on an instrument’s arc in 1775. This instrument is a smaller version of the Hadley octant in which the “double
reflecting” principal was introduced by Hadley to the Royal Society in London in 1731. Hadley began selling octants
shortly thereafter which had a vertical dimension of 17″ or more. The instrument is 15 3/4 inches on the vertical. It
has been recently polished and lacquered, and is in a remarkable well preserved condition considering its 234 year age
and use at sea. You may read the Condition Statement for details.
The cross member, which seems
to be original is unmarked. This is not as unusual as many instruments were made to allow the retailer or an owner to
imprint their name which frequently was not done
MARKINGS: Using a magnifier you can clearly see an anchor
between 45 and 50 degree position on the arc. The anchor is the well known mark of Jessie Ramsden, perhaps the most famous
of all English instrument makers. It was Ramsden who invented the dividing machine which allowed for the precision indexing
of degrees on an instrument’s arc.JESSE RAMSDEN, ONE OF ENGLAND’S MOST IMPORTANT INSTRUMENT MAKER’S HISTORY: Jesse
Ramsden (1735-1800)Ramsden was one of the most famous English scientific-instrument makers of the second half of the eighteenth century. In
1775, he invented a semi-automatic dividing machine, capable of marking graduated scales on sextants and other nautical and
astronomical instruments for his own instruments and provided the same to other mathematical instrument makers. He developed
improvements in the manufacture of sextants, theodolites, barometers, micrometers, and countless other devices. One of the
most important instruments built by him is the great astronomical circle of the Palermo Observatory. In 1786, elected fellow
of the Royal Society of London and, eight years later, member of the Imperial Academy of Saint Petersburg. In 1795, won the
Copley Medal, the highest scientific award of his time: the prize was established in 1736 by the Royal Society, thanks to
a bequest from Sir Godfrey Copley.What can be clearly seen is the anchor’s stock and flukes and with less clarity,
an “F” to the left of the stock and a “P” to its right.There were many instrument makers whose names began with
these letters, but most of them made telescopes, microscopes and chronometers. We could find only one who made octants. Peter
Feathers, a Scotsman who operated from High St. and Dock St. in Dundee from 1842 until 1872. In 1873 he took in his son as
a partner, but this is way too late to be making such a large octant. Therefore, the most likely maker of the arc is the most
obvious, Jessie Ramsden, and the shop that did the assembly of the frame and working parts is lost to history.
Maker’s mark a “F” Anchor “P” between 50° & 45°Marked in pencil in a European hand on the center ebony upright is “J 69 over
18 space 44”. The 18 44 is not written as a date.
It has a early style Ebony frame, flat brass
index arm, graduated arc and vernier, and precisely machined bronze fittings. The three
shade glass assembly is movable for placement at either the index mirror position or below at the secondary position where
the third mirror allows for the taking of “back sights”.For details on how we dated this instrument, see below.
The metal fittings
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OUR QUALIFICATIONS: We are one of the few company’s still selling