AN INSTRUMENT OR QUADRANT FOR TAKING THE ALTITUDE OF THE SUN OR MOON AT SEA OF LAND, BUT MORE ESPECIALLY AT SEA, BY REFRACTION, IN WHICH, BY MEANS OF A LENS ADAPTED THERETO AS TO ADMITT THE RAYS TO PASS THRO' OR BY IT IN A BACKWARD OBSERVATION
Year: 1750

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, GEORGE
ADAMS, of Fleet Street, London, Mathematical Instrument Maker, and
RICHARD JACK, late of the Parish of St. Martin, but now of the Parish of Saint
James, Westminster, in the County of Middlesex, Gentleman, send greeting..
WHEREAS His present Majesty King George the Second, by Letters
Patent under the Great Seal of Great Britain, bearing date the Twenty-fifth
day of May last past, reciting, that the said George Adams and Richard Jack
had, by their Petition to His Majesty, represented that they had, by long study
and at a very great expence, contrived "AN INSTRUMENT OR QUADRANT FOR TAKING
THE ALTITUDE OF THE SUN OR MOON AT SEA OF LAND, BUT MORE ESPECIALLY AT SEA,
BY REFRACTION, IN WHICH, BY MEANS OF A LENS, THE OBJECT IS THROWN UPON THE
ARCH OF A CURVE, AND IS MADE TO COINCIDE WITH THE HORIZON BEEN THRO' THE
SAID ARCH, OR ANY SUBSTANCE 50 ADAPTED THERETO AS TO ADMITT THE RAYS TO
PASS THRO' OR BY IT IN A BACKWARD OBSERVATION, AND THAT THE SAID ARCH IS BY
A PARTICULAR CONTRIVANCE RENDERED MOVEABLE, SO AS IN ALL POSITIONS OF THE
INSTRUMENT TO PRESERVE THE COINCIDENCE OF THE OBJECT AND HORIZON, AND FOR
OTHER PURPOSES; THAT THEY HAD ALSO INVENTED A REFRACTING TELESCOPE OF A
NEW CONSTRUCTION, CONSISTING OF FOUR SPHERICAL LENSES, WHICH MAY BE ALL OF
DIFFERENT FOCAL DISTANCES, OR ONLY TWO OF DIFFERENT FOCAL DISTANCES, AND THE
OTHER TWO OF EQUAL FOCAL DISTANCES, WHICH MAY BE USED WITH OR WITHOUT THE
QUADRANT, WHEREBY DISTANT OBJECTS ARE BEEN DISTINCT AND LARGER THAN WITH
TELESCOPES OF THE ORDINARY CONSTRUCTION WHICH ARE TWELVE OR FIFTEEN FEET
LONG, ALTHO THE SAID TELESCOPE SHOULD NOT EXCEED FOUR FRET IN LENGTH, AND
EVEN BETTER THAN BY REFLECTING TELESCOPES OF A CONSIDERABLE LENGTH AND
PRICE, AND FOR OTHER PURPOSES, BY MEANS WHEREOF THEY WILL BE OF CONSIDERABLE

page_text: UBE IN NAVIGATION & ASTRONOMY, AND CONSEQUENTLY OF GREAT SERVICE TO THE
ROYAL NAVY, AS WELL AS TO THE TRADE AND NAVIGATION OF THE KINGDOM,"
and praying His Majestie's Letters Patent for the sole use thereof; His
Majesty did thereby give and grant unto the said George Adams & Richard
Jack, their executors, admors, and assigns, His especial licence, full power,
priviledge, and authority, to make usc, exercise, and vend their said Inventions
within England, Wales, or Berwick-upon-Tweed, to have, hold, exercise,
and enjoy the same for the term of fourteen years from the date thereof;
in which said Letters Patent is contained a proviso that if the said George
Adams and Richard Jack should not particularly describe and ascertain the
nature of their said Inventions, and in what manner the same are to be
performed, by an instrument in writing under their hands and scals, or the
band and seal of one of them, and cause the same to be inrolled in the
High Court of Chancery within four kalendar months next after the date of
the said Letters Patent, that then the said Letters Patent, and all advantages
thereby granted, should cease and become void.
NOW KNOW YEE, that the said George Adams and Richard Jack, in
pursuance and performance of the said proviso, do hereby describe the nature
of the said Inventions, and in what manner the same are to be performed,
as follows (that is to say) :—
The quadrant is contrived for taking the altitude of the sun or moon at sea
or land by refraction, in which, by means of a lens placed on the one of the
radii, the object is thrown upon the arch of a curve, and is made to coincide
with the horizon seen thro' the said arch, or any substance so adapted thereto
as to permit the rays to pass thro' or by it in a backward observation, and the
said arch is by a particular contrivance of a lever rendered moveable, so as in
all positions of the instrument to preserve the coincidence of the object and
horizon. The same effects may also be produced in a forward observation by
means of a double or treble refraction from lenses, one lens being placed, as
before, on one of the radii, which throws the image of one of the objects on the
aforesaid arch of a curve, or any substance so adapted thereto as to permitt the
rays to pass through or by it. On the moveable index is placed another lens,
which also throws the other object on the aforesaid arch of a curve, or any
substance so adapted thereto as to permitt the rays to pass through or by it.
These two images or objects are seen thro' an eye lens, placed on the index a
little beyond its centre. Each of the object lenses aforesaid, when the instru-
ment is adapted both for the backward and forward observation, have a
segment cutt off, and also the object lense, which is placed upon the index, is
perforated in its centre. The pendant mirrour is suspended by pivotts, and is
preserved in its due position by means of one, two, or more ballance weights,

page_text: which also are pendant on perpendicular points. With the magnetick compass
the sun's magnetick azimuth may be taken by the shadow of a perpendicular
wire fixed over the center of the cap on which the needle- is suspended when
the sun hath but a small elevation above the horizon, and at all greater
altitudes by fixing the aforesaid magnetick compass to the quadrant aforesaid..
The telescope is composed of four spherical lenses, which may be all of
different focal distances, or two of the three eye lenses of the same focal
distance but different from the focal distances of the other two, which are also
of different focal distances. The spherical lenses themselves may be either all
double convex, or the three next the eye may be all plano-convex, or two of
them either double or plano-convex, and the other a meniscus lens. These
four lenses are placed in various tubes, and the two nearest the eye are in
tubes much smaller than the other. In the construction of this telescope the
distances of the lenses from each other are varied according to the distance of
the object and focal distance of the observer's eye, and in all cases whatsoever
the distance of any two of the lenses never exactly correspond to that of the
sum or difference of their focal distances, as in the common refracting telescope,
whose magnifying power is limited to the simple proportion of the focal
distance of the object lens to the focal distance of the eye lens, or of either of
the eye lenses; whereas in this new-invented telescope the diameter of an
object is magnified more than what it appears to the naked eye, in a ratio or
proportion compounded directly of the focal distance of the object lens to the
focal distance of the first or nearest eye lens, and of the focal distance of tho
second eye lens to the third, or that nearest the eye, and of the refracting
power of the eye lens and of the reciprocal ratio or proportion of the distance
of the lenses from each other, when the telescope is adjusted to any particular
object, to the sume or difference of their respective focal distance.
In witness whereof, the said George Adams and Richard Jack have
hereunto sett their hands and seals, the Thirty-first day of August,
in the twenty-fourth year of the reign of our Sovereign Lord George
the Second, by the grace of God of Great Britain, France, and Ireland
King, Defender of the Faith, and so forth, and and in the year of
our Lord One thousand seven hundred and fifty.

page_text: AND BE IT REMEMBRED, that on the said Thirty-first of August,
the aforesaid George Adams and Richard Jack came before our Lord the
King in His Chancery, and acknowledged the Writing aforesaid, and
every thing therein contained and specified, in form above said. And also
the said Writing was stamped according to the Statuto mado in the sixth
year of the reign of the lato King William and Queen Mary, and so forth.
Inrolled the First day of September, in the said twenty-fourth year of the
reign of King George the Second.
INTIY LLO