AN ASTRONOMICAL EQUATORIAL INSTRUMENT
Year: 1775

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JESSE
RAMSDEN, of Piccadilly, in the Liberty of Westminster, in the County of
Middlesex, Optician, send greeting.
WHEREAS His most Excellent Majesty King George the Third, by His
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Thirtieth day of December, in the sixteenth year of His reign,
did give and grant unto me, the said Jesse Ramsden, His special licence, full
power, sole priviledge, and authority, that I, the said Jesse Ramsden, my
executors, administrators, and assigns, should and lawfully might, during the
term of years therein expressed, make, use, exercise, and vend, throughout that
part of His Majesty's Kingdom of Great Britain called England, the Domi-
nion of Wales, and Town of Barwick-upon-Tweed, my Invention of "AN
ASTRONOMICAL EQUATORIAL INSTRUMENT;" in which said. recited Letters Patent
is contained a proviso obliging me, the said Jesse Ramsden, by writing under
my hand and seal, to cause a particular description of the nature of the
said Invention, and in what manner the same is to be performed, to be inrolled
in His Majesty's High Court of Chancery within four calender months after
the date of the said recited Letters Pattent, as in and by the said Letters
Patent and the Statute in that behalf made, relation being thereunto
respectively had, may more and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso and in pursuance
of the said Statute, I the said Jesse Ramsden, do hereby declare that my said
Invention is composed, made, and performed in manner and consists of the
articles herein-after mentioned, that is to say:-
First, the form of the æquatorial circle and its supports. Second, the
application of a spirit level to the telescope. Third, an apparatus for giving
and conecting the effects of refraction and parallax. Fourth, a prismatic
eyeglass. Fifth, a reflecting micrometer, which requires no additional
glasses.
First, the æquatorial circle is dished, and the supports of its transverse axis
bent in the form of a scroll, so as to admit of the telescope to be set parallal
to the polar axis for any latitude, as represented in the annexed Figure.
Secondly, in all the æquatoriol instruments that have been made, spirit levels
for adjusting the position of the instruments are applied to the azimuth and
æquatorial circles only, but as defects may arise between them and the line of
collimation which they can neither indicate or conect, an additional spirit level
is in à my construction immediately applied to the telescope and suspended on an
axis with adjustments to bring it perfectly parallel to the line of colimation,
so as to become a checque on every adjustment whatever of the æquatorial in
all possible horizontal positions of the telescope. The manner in which I
have generally applied these levels is represented by the annexed Figure, but
these may be varied as circumstances may require.
Thirdly, the eye tube of the telescope in my æquatorial has a motion round
its axis by a rack and pinion, so that by means of a circular spirit level one of
the cross wires in the tube may be rendered vertical and the other horizontal
in any possible position of the telescope; and a graduated plate, which carries
round the eye tube, shews the angle of position; the same circular level also
shews, by means of a small graduated quadrant, the elevation of the telescope
above the horizon, and the corresponding refraction; and the eye tube with the
cross wires have another motion, so as to be depressed or elevated by a micro-
meter screw as much as the apparent place of the object differs from its true
place, and the instrument will then shew the true elevation of the object as
if no refraction took place.
Fourthly, in some positions of the instrument it becomes inconvenient to
look thro' a telescope of the usual construction, in which cases I apply an
eyeglass which unites the properties of the prism with those of the common
eyeglass, and the light being thus reflected by the back surface of the glass,
the object is conveniently viewed at right angles to the axis of the telescope.
Fifthly, when reflecting telescopes are used either with the æquatorial or

page_text: separately, I have invented a micrometer which requires no additional glasses
to those commonly used in the telescope, by having the small speculum cut
thro' its center so as to divide it into equal parts, each of which hath a
motion round a center different from the center of its anvature, and in direc-
tions contrary to each other; and as each half of the speculum will thus form
a distinct image of the object when the extremities of these two images appear
in contact, the inclination of the parts of the speculum with each other will
give the angular diameter of the object.
Each of the above Inventions, altho' independant of each other, is, never-
theless, essentially necessary towards perfecting the æquatorial instrument, and
each may advantageously be used seperately and independant of the æquatorial;
and the principals of these several Inventions may be applied in varios modes
as circumstances may require or fancy suggest without losing the characteristics
of properties already mentioned.
In witness whereof, I have hereunto set my hand and seal, this Twenty-
HANDLEY.
ROBERT GATE HANDLEY.
AND BE IT REMEMBERED, that on the Twenty-seventh day of April,
in the year of our Lord 1776, the aforesaid Jesse Ramsden came before our
said Lord the King in His Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form
above written. And also the Specification aforesaid was stampt according
to the tenor of the Statute made in the sixth year of the reign of the late
King and Queen William and Mary of England, and so forth.
T AL
Inrolled the Twenty-seventh day of April, in the year of our Lord One
thousand seven hundred and seventy-six.

page_text: 1: Finger sarews wine
BS Azimuth Circle.
CS Supports which sustain the transverse
axis of the equatorial circle.
D The Polar Axis passing thro'the transverse
aais, on the end of which is
E a weight that ballances the upper parts.
of the instrument.
F The Equatorial Circle.
GS. Supports for the axis of the Declination
Circle.
Its axis J. The Declination Circle.
The Hanging Level
K The Telecope
The Quad of the Apparatus for Refraction
M The eye tube...
N The ballance for the Telescope.
m Circular Level for the apparatus for