IMPROVEMENTS IN SEXTANTS AND OCTANTS.
Year: 1877

page_text: LETTERS PATENT to George Wilson Heath, of Glen View House, Crayford, in
the County of Kent, for the Invention of "IMPROVEMENTS IN SEXTANTS AND
OCTANTS.
"
Sealed the 6th October 1877, and dated the 2nd May 1877.
"
PROVISIONAL SPECIFICATION left by the said George Wilson Heath at the
Office of the Commissioners of Patents on the 2nd May 1877.
GEORGE WILSON HEATH, of Glen View House, Crayford, in the County of Kent.
IMPROVEMENTS IN SEXTANTS AND OCTANTS."
As a matter of practical experience in the manufacture of metal sextants and
octants with inserted graduated pieces of ivory or bone, it has been proved
that the action of varied temperatures produces contraction or expansion of the
scale to so large an extent that a true reading of the same is almost impossible.
It has also been proved that when sextants and octants have been made of ebony
or hard wood, with ivory or bone inserted and cemented to the wood, that the
affinity between the two is such that contraction or expansion is either entirely
removed or reduced to an incalculable minimum.
It has also been proved that ivory and bone are subject to discolouration and
other facial derangements, thereby necessitating a constant return to the original
manufacturer for re-fitting and re graduation, and entailing both loss of time and
large expense.
My improvements relate,-
Firstly. To the fixing of ivory arcs to metal sextants and octants of all classes, in
such manner that the action of varied temperatures upon the metal shall not effect
the essential fixture of the ivory inlaid.
Secondly. To so placing the arc and vernier in the limb and index that at any
time they can either of them be easily removed by an almost inexperienced hand,
and fresh ones replaced without the return of the instrument to the original manu-
facturer for re-graduation.
These results are accomplished as follows:- -The metal arc of the instrument is
formed with a deep groove capable of receiving an arc of ebony or other hard wood,

page_text: within which a strip of ivory or bone is embedded and cemented, pinned, or other-
wise secured to the hard wood, the arc of hard wood being about three-eighths of an
inch thick, and six-eighths of an inch wide, and the ivory or bone are being so
inlaid as to leave a margin of ebony or hard wood on either side of about one-
eighth of an inch in width.
In the second place these composite arcs are made removeable, being clamped
from the under side on to the metal arc by six or more screws. The graduated
vernier is also attached to the index by two screws instead of the usual pinning.
The groove of the metal arc and the chamfer of the vernier slot on the index are in
all cases made exactly from one pattern.
The holes in both metal arc and index vernier slot are made in all cases the same.
The corresponding holes in the composite ebony and ivory are and graduated vernier
are also in all cases made to correspond.
The mounting and adjusting of the instruments are.in all cases the same, thus
allowing the removal and introduction of a spare graduated composite arc and
vernier whenever and wherever they may be needed."
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said George Wilson Heath in the Great Seal Patent Office on the
2nd November 1877.
"
GEORGE WILSON HEATH, of Glen View House, Crayford, in the County of Kent. 2
IMPROVEMENTS IN SEXTANTS AND OCTANTS."
As a matter of practical experience in the manufacture of metal sextants and
octants with inserted graduated pieces of ivory or bone, it has been proved that the
action of varied temperatures produces contraction or expansion of the scale to so
large an extent that a true reading of the same is almost impossible.
It has also been proved that when sextants and octants bave been made of ebony
or hard wood, with ivory or bone inserted and cemented to the wood, that the
affinity between the two is such that contraction or expansion is either entirely
removed or reduced to an incalculable minimum.
2
It has also been proved that ivory and bone are subject to discolouration and 3
other facial derangements, thereby necessitating a constant return to the original
manufacturer for re-fitting and re-graduation, and entailing both loss of time and large
expense.
My improvements relate,-
Firstly. To the fixing of ivory arcs to metal sextants and octants of all classes, in 3
such manner that the action of varied temperatures upon the metal shall not affect
the essential fixture of the ivory inlaid.
Secondly. To so placing the arc and vernier in the limb and index that at any
time they can either of them be easily removed by an almost inexperienced hand,
and fresh ones replaced without the return of the instrument to the original manu-
facturer for re-graduation.
These results are accomplished as follows:-The metal arc of the instrument is
formed with a deep groove capable of receiving an arc of ebony or other hard wood,
within which a strip of ivory or bone is embedded and cemented, pinned, or other-
wise secured to the hard wood, the arc of hard wood being about three-eighths of an
inch thick, and six-eighths of an inch wide, and the ivory or. bone arc being so
inlaid as to leave the margin of ebony or hard wood on either side of about one-
eighth of an inch in width.
In the second place these composite arcs are made removable, being clamped from
the under side on to the metal arc by six or more screws. The graduated vernier is
also attached to the index by two screws instead of the usual pinning.

page_text: The groove of the metal arc and the chamfer of the vernier slot on the index are
in all cases made exactly from one pattern.
The holes in both metal arc and index vernier slot are made in all cases the same.
The corresponding holes in the composite ebony and ivory arc and graduated vernier
are also in all cases made to correspond.
The mounting and adjusting of the instruments are in all cases the same, thus
allowing the removal and introduction of a spare graduated composite arc and
vernier whenever and wherever they may be needed.
The annexed Drawing shows at Figure 1 an octant constructed according to my
Invention. The metal limb or arc, of which an end view is shown at Figure 2, is of
a trough-like form and of considerable depth; its sides are somewhat inclined, and
it is adapted to receive a stout arc of hard wood, by preference, well seasoned ebony,
a material which is not liable to contract or expand from variations of temperatures
and climate. I prefer to fix the ebony are in the trough by means of a number of
wood screws entering it through the bottom of the trough. The holes for the
screws are carefully prepared before-hand, they are bored to a gauge so that they
may exactly correspond to the holes in the metal trough-like arc of the instrument.
An under side view of the ebony arc is shown at Figure 3. The face of the ebony
arc is inlaid with a veneer of ivory, which I prefer to secure by means of a strong
cement such as is not liable to be affected by moisture; marine glue is suitable.
The arc is graduated upon the ivory in the usual way after it has been inlaid into
the ebony. The vernier is fixed to the radial arm of the instrument by two brass
screws, as the Drawing indicates. The vernier is shown separately at Figure 4.
In instruments thus constructed, if the graduations should become defaced by
accident or otherwise, a spare are and vernier can be fitted without the necessity
for returning the instrument to the maker.
What I claim is, the construction of the arcs of sextants and octants, substantially
in the manner described.
In witness whereof, I, the said George Wilson Heath, have hereunto set my
hand and seal, this First day of November, in the year of our Lord One
thousand eight hundred and seventy-seven.
GEORGE WILSON HEATH. (L.S.)