See our current inventory of Antique sextants and ocatants here
Ca 1778

PRESENTED is a late 18th C. mariner’s octant
made by the two famous Troughton brothers, John and Edward. John, the elder brother, was trained as an instrument maker by
his uncle and became well known as an instrument maker who specialized in dividing the arcs of instruments for other craftsman
which at that time he did by hand. In 1773 at age 20, Edward joined John as apprentice. Between 1775 and 1778, John constructed
his own dividing engine, similar to the one of Jessie Ramsden’s. The evenness of the spacing and markings on the ivory arc
suggest that this instrument was one of the first made by this machine.
The Troughton business had a shop at 136 Fleet St., London. The
business flourished and Edward became a partner with his brother who died shortly thereafter in 1788. This event was followed
by Ramsden’s death in 1800 leaving Edward Troughton to quickly become England’s leading maker of instruments. For example,
he designed the “pillar” sextant in 1788, the dip sector, a marine barometer, and reflecting circle in 1796 all of which is
after the date of this octant. One of his most important contributions built on his brother John’s and Ramsden’s methods of
dividing a circle, and in 1809 he was awarded the Copley Medal of the Royal Society for his invention which achieved greater
accuracy. He was elected a member of the society in 1810.
This outstanding example of Edward and John’s work is the
most beautifully made instrument that we have ever had the pleasure to offer. It has an
ebony frame,
flat brass index arm, ivory graduated arc and vernier, and exquisitely made bronze fittings.

             Troughton, London
  Unusual Oak case, rounded corner

The metal fittings are precisely machined to a level of smoothness and finish that makes this instrument a true work
of art and sets it apart from all other octants of this period. It is truly magnificent.

It is housed in a fan shaped Oak wood case with a green felt liner,
and polished brass trim. The top of the case is curved, and the panels are fitted using the tongue and grove method, again
a rarely seen and unusual feature. The initials “MI” are painted in white on its top.

The arc measures from – 5 to plus 95 degrees. It has a flat brass
index arm measuring a long 13 3/4 inches, with a clamping mechanism rather than a tangent screw. The horizon mirror is mounted
on an adjustable turntable. Its base can be rotated by loosening a screw which locks the mirror’s position. Note the early
form ivory vernier scale, reading from right to left from 20 to 0 arc minutes, a two hole peep sight with “shade glass”, and
moveable three sun shades which serve both mirrors on the frame. The index mirror is of very large size, and is in excellent
All of these features date the instrument before the turn
of the 18th century, likely Ca 1775. See Peter Ifland’s comprehensive sextant work, “Taking the Stars”. particularly
figure 64, page 57.
Some time after 1780, the addition of a tangent screw, not on
this instrument, allowed for fine adjustment and represented one of the two major changes in the basic operation of the octants
and sextants for the next 150 years! The second was the fitting of telescopes. As was the practice with octant’s of this larger
size, only peep sights were fitted. Later a handle was added. The history of the brother’s working together, and all of these
tell tales indicate it is one of the earliest of that type.

Finely made fittings, large index mirror
The machinery

CONDITION: The instrument is in exceptional condition in all respects.
The ivory graduated arc, and all its hardware are in like new condition and of the highest quality. It was lacquered some
time ago, and has a wonderful patina of age under. All three bronze legs are present. It has the ivory pad on back, but is
missing is the small ivory scribe. Both the index and horizon mirror are in exceptional condition and show as near new. The
Oak case, has a lengthy age crack down its length, but is rigid, and is otherwise in excellent condition.

All in all, a ver rare,
desirable, and very special example from one of England’s most famous instrument makers


  • Arc reads – 5 to +95 degrees
  • Length of frame 13 3/4″ long
  • Width of frame at arc 11 ” wide
  • Index mirror 50 x 34 mm
  • Horizon mirror – 20 x 24 mm
  • Three shade glasses
  • Two Peep sights
  • Weight 2 Lbs 12 oz

CREDENTIALS: We are one of the few people on the web selling
navigation instruments that know anything about them. For purposes of judging whether my opinion counts, I 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. I am
also a retired Master Mariner, and held a U.S. Navy “D” Qualification as a Senior Skipper – Oceans