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EARLY PERIOD ENGLISH BACK SIGHT OCTANT
JESSIE RAMSDEN ANCHOR IMPRINT Ca 1795
PRESENTED is a mariner's octant made
during the first half of the 18th Century. It is fitted with two horizon mirrors and two peep sights, the lower
set being for taking “back sights“.It has the highly desirable imprint of a partial anchor with initials
on either side on the arc between 45°; and 50° which is known to be that of Jessie Ramsden, one of England's foremost instrument
makers. Jesse Ramsden invented the dividing machine allowing for the precision marking of degrees on an instrument's
arc in 1775 and also made these arcs for others. The accuracy and sharpness of the arc's numerals suggest that this instrument
was made by an advanced instrument maker, one who would stand at the top of his trade.
This octant is marked
J.B. Le Roy on the crossbar with the name listed in Webster's Database of Instrument makers with only one example dating to
1820. The instrument is 13 3/4 inches on the vertical which is still
oversize for octants, but smaller than the typical Hadley style octant of 17“. It was Hadley that invented the "double
reflecting" principal introducing it to the Royal Society in London in 1731.
It is in its natural state with
a mellow patina of age that has developed over the last 216 years and is remarkably well preserved considering
age and use at sea. Please read the Condition Statement for details.
The original ivory cross member ivory is marked,
I.B. Le Roy, Guernsey
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.
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Arc - engraver's mark between 50° & 45° |
MARKINGS: You
can clearly see the flukes of an anchor between 45 and 50 degree position on the arc. With the aid of a loupe
you can make out an initial on either side of the anchor. This mark is best known as that of Jessie Ramsden. Ramsden
is the English instrument maker who invented the dividing machine which allowed for the precision indexing of degrees
on an instrument's arc.
Inside the case are eight notations in pencil which solve Local Apparent Noon sights for
latitude. In addition is, “Bark Sunette“, and the name of the master which is illegible. There also
is an H. Duren, 39 Burling Slip, New York, instrument maker's label. Duren was active there in the 1850's,
but this octant, made in England, predates that by a wide margin.
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Sighting machinery looking forward | |
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Sighting
machinery looking aft | |
The metal fittings are precisely machined, and makes this instrument a work of engineering
excellence for so early a period .
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DATING THE INSTRUMENT: The ivory
arc measures from - 5 to plus 95 degrees on a Ebony frame which is in excellent condition. It is known that Mahogany
went out of use in favor of Ebony some time after 1750. The octant has a flat brass index arm without a stiffening
brace that measures 13 3/4 inches to the bottom of the index arm. Tangent screws began replacing finger clamps in
the last quarter of the 18th Century. There are two horizon mirrors, each
mounted on an adjustable turntable where the base can be rotated by loosening a screw which locks the mirror's position. There is
a single set of three shades which may be moved from the upper to lower position. The ivory vernier scale, reads from right
to left from 20 to 0 arc minutes. There are two peep sights. The adjustable tangent screw, followed the use of the
index arm clamp which ended around the last quarter if the 1700's.
All of these features date the instrument after 1750 and before 1800.
See Peter Ifland's comprehensive sextant work, "Taking the Stars". particularly figure
64, page 57.
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Old style vernier reading from 0 at right | |
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Period stair step keystone case | |
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VIEW THE GALLERY BELOW FOR MORE PHOTOGRAPHS
CONDITION: The instrument is in excellent condition. The graduated
arc, and all its hardware are in working order. All three bronze legs are original. It is missing the
original ivory pencil on the cross bar as are most instruments of this age. All three mirrors have most
of their silvering, but show their age. The machinery is all present.
The Case is the early style “stair
step“, keystone design of this period. Both the top and bottom have age cracks, but everything is secure. The inside
has an H. Duren, 39 Burling Slip, New York, instrument maker's label pasted over the remnants of a second
label. There numerous pencil notations in the inside which are discussed under markings. It is strong and
sturdy, and the octant fits as it should. There are a number of different coats of paint in Colonial greens. There is a
lock, but no no key.
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Instrument
in case. Note label and age cracks |
All in all, a rare,
desirable, and special example of an early Hadley style octant.
DIMENSIONS:
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Arc reads - 5 to +95 degrees
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Length of index arm 13 3/4" long
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Width of frame at arc 11 1/4 " wide
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Index mirror 43 x 32 mm
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Horizon mirror - 27 x 18 mm
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Back sight mirror - 27 x 18 mm
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Three movable shade glasses
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Two Peep sights
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Weight octant 2 Lbs 9 oz
 OUR 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 also a retired Master Mariner, and held a U.S. Navy "D" Qualification as a Senior Skipper - Oceans. From 1995 through 2000, he served as a Varsity Offshore Sailing Team coach at the U.S. Naval Academy.
OUR UNCONDITIONAL
NO NONSENSE GUARANTEE: If not completely satisfied with your purchase it may be returned, if without damage,
within three days of receipt in its original packaging. Return items must be insured for their full value. Only a prior email
authorization by us for the return is required. Shipping charges are included in this offer if the error is due
to our fault.
International buyers welcome, but must inquire first. We have
satisfied customers in Argentina, Australia, Austria, Belgium, Bermuda, British Virgin Islands, Canada, Chile, China, Czech
Republic, Democratic Republic of Congo, Denmark, Estonia, England, France, Germany, Greece, Holland, Hong Kong, Hungary,
Iceland, Ireland, Israel, Italy, Japan, Kuwait, Luxembourg, Latvia, Malaysia, Martinique, Mexico, New Zealand, Norway,
Nova Scotia, Panama, Poland, Portugal, Puerto Rico, Romania, Saudi Arabia, Scotland, Singapore, Spain, Sweden, St. Maarten,
Switzerland, Thailand, Turkey, United Arab Emirates, USVI and the Eastern Caribbean.
ACCEPTED FORMS
OF PAYMENT are Bank wire transfer, cashier's check, money order, or personal check in which case the item will be
held until cleared. No credit cards or PayPal accepted on this item.
This early octant is a special find for someone who appreciates a rare 18th Century instrument.
Copyright
2011 by Land And Sea Collection™, All Rights Reserved
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