Ca 1777 


PRESENTED is a superior quality late 18th C. mariner’s
three mirror octant with ebony frame. ivory graduated arc and vernier, and bronze fittings. We can say this instrument is
of museum quality without reservation. The arc measures from – 5 to plus 95 degrees. In the center of the ivory
degree’s scale between 45 and 50  degrees is inscribed in script “SBR” identifying this instrument
as that of Spencer Browning & Rust, of London. But over it is the mark of a fouled anchor which belonged to
one of Britain’s most famous instrument maker’s Jesse Ramsden. Among other things, Ramsden was the first to invent a dividing
machine which enabled much more precise divisions. He was given a generous 615 pound award by the Board of Longitude for
this invention which required that he make the results available to ten other instrument makers for a fee.
PROVENANCE: The octant was handed down in the family of the Captain
Benjamin Walker of South Eastham, MA. Benjamin Walker’s DOB and DOD are unknown. He was one of teh original six settlers of
Eastham. It was given by him to his son John Walker, ( 1857-1948), and then by him to the grand daughter of his older brother.
John Walker was buried in Winthrop, ME. A note to this effect accompanies the instrument.


Spencer Browning Rust worked
in London from 1724 to 1840 when the name was changed to Spencer Browning & Co. after the death of Ebenezer
Rust.  The successor, Spencer Browning had offices at a number of addresses on Wapping High
Street, London and were in business until 1870. They had an early dividing machine and
inscribed arcs for others.
Ref: Gloria Clifton, Directory of
British Scientific Instrument Makers 1550-1851
(London, 1995), p. 261.

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.
beautifully made octant has a brass index arm without a brace that measures 14 inches long counting the tab, which
is less than normal for this period. This is a result of Ramsden’s advanced method of dividing the arc which allowed
for the reduced size. The top horizon mirror is mounted on an adjustable turntable. The base can be rotated by adjustment
screws on the back side. The lower mirror adjusts the same way and has a second peep sight. The lower unit is used for
taking back sights, and were only fitted to very early octants.
Note the early form ivory vernier scale, reading from right to
left from 0 to 20 arc minutes, a two hole peep sight with “flap” for the horizon mirror plus a single peep sight for the backsight
mirror, and the moveable three sun shades which serve both mirrors on the frame. There is no tangent screw on early instruments
only a clamp. All of these features date the instrument before the turn of the 19th century, likely Ca 1777 since
Ramsden’s dividing machine was invented in 1775.

               Early style
stair step keystone case interior
INSTRUMENT CONDITION: The sextant appears in its last used condition
having been maintained by mariners who too excellent care of it. The index mirror is in much better condition than might
be expected with little loss of silvering. age. The horizon mirror has lost much of its silvering, but is in otherwise
good condition. The ivory is in perfect condition, except for some age darkening at the ends. The engraving is sharp
and distinct. The index arm clamp is complete. The shade glasses are complete. Everything is in good working order. The
entire instrument and ebony frame shows as near new. The instrument has all its original machinery. The only thing that
has been lost over the years is the ivory pencil holder that has been replaced by  a wood facsimile.

THE CASE: The stepped “keystone” solid Oak case is in excellent
condition, but has some age cracks top and bottom. It has its original New England colonial blue coloring. There
is no lock or key, but there is a cover plate.
 Maker’s name
   Jesse Ramsden’s anchor imprint at 55 degrees
       The machinery. Back sight to right
           Peep sight & horizon mirror               
THE LABELS: The large label with the colonial blue
wash over is mostly illegible. What can be seen is that it belongs to a mathematical instrument maker with a Boston address.
The last name was Dutom or Duton which is not listed in any of the traditional references.
The smaller label is that of Fredrick W. Lincoln, Jr. who was
the grandson of Paul Revere. Lincoln was born in Boston on February 17, 1817, a grandson of Paul Revere, and became mayor
of Boston during the Civil War. He began business under his name as a nautical instrument maker in 1839. In 1858, Lincoln’s
apprentice, Charles Hutchinson became a partner and the firm name was changed to F. W. Lincoln, Jr. & Co. Hutchinson bought
out the business in 1883. Therefore, this octant was either serviced by the Lincoln firm or resold by them sometime between
1839 and 1858.
The smaller label was originally pasted over the larger label and the
four dots of glue can be seen in the corners. It was lying loose when the instrument was received with corresponding glue
residue on its backside.
A highly
desirable and worthwhile collaboration from two of the better known English instrument makers, and with a know
history of ownership.
  • Arc reads – 5 to +95 degrees
  • Length of frame 14″ 
  • Width of frame at arc 11″ wide
  • Index mirror 48 x 35 mm
  • Horizon mirror –
  • Back sight Mirror 22 x 22 mm
  • Three shade glasses
  • Two Peep sights
  • Weight    2 Lbs 8 oz octant   4 lbs 8 oz total

QUALIFICATIONS: We are one of the few company’s still selling navigation
instruments that know anything about them. For purposes of judging whether Joel’s opinion counts, he was the editor
of the chapter on sextants of the 1977 Edition of “Bowditch”, The American Practical Navigator, NAVPUB 9; a member of the
U.S. Naval Academy Navigation Symposium Board, 1975 -1978; the author of a book on marine sextants, Cornell Maritime Press,1975,
and the founding president of Nautech Maritime Corporation which partnered with Tamaya of Japan in the introduction of the
MS 733 Spica, the MS 833, Jupiter, MS 933 Venus sextants and the famous NC-2 navigation computer, in the U.S. market. Joel
is a retired Master Mariner, and held a U.S. Navy “D” Qualification as a Senior Skipper – Oceans.
six years he was a Varsity Offshore Coach at the U.S. Naval Academy.
Rarely do you find an instrument that
is that is 167 years old in this original condition with a perfect historic label. A superior addition to any collection.

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