IMPROVE- MENTS IN OPTICAL AND MATHEMATICAL INSTRUMENTS."
Year: 1853

page_text: LETTERS PATENT to Isaac Davis, of 119, High Holborn, in the
County of Middlesex, Optician, for the Invention of "IMPROVE-
MENTS IN OPTICAL AND MATHEMATICAL INSTRUMENTS."
PROVISIONAL SPECIFICATION left by the said Isaac Davis at the
Office of the Commissioners of Patents, with his Petition, on
the 26th January 1853.
I, ISAAC DAVIS, of 119, High Holborn, in the County of Middle-
sex, Optician, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN OPTICAL AND MATHEMATICAL INSTRUMENTS" to be as
follows:-
A new application for determining distances, and increasing or
decreasing the field of view, by means of cross wires applied to the
diaphragm of the eye draw, or to the eye glass of a telescope, or
one cross wire, or a narrow blank, or an opening and a blank on
each side, and two holes made in the blank part to admit light, and
a cylindrical bar A, Fig. 1, placed parallel to a base or platform B, C,
erected on a theodolite or other suitable stand. This base or plat-
form may have a horizontal or swivel motion D.
The telescope

page_text: is affixed to this bar by means of a square box, so as to move easily
along, and is kept in position by a support travelling on the platform,
or by any other suitable means.
Either the bar or platform may
be divided into a graduated scale, by means of which, in combination
with the cross wires, the position of an object may be determined;
or a micrometer screw, or a combination of screws, may be used. If
a wheel be attached to the micrometer screw, it must be of the same
height as the cylindrical bar is fixed above the platform, and its size
must be determined according to the field of view that is used. It
may also be graduated.
One or two telescopes may be used, according to the requirements
of the instruments. Instead of the platform and the cylindrical bar,
a tube line or rough bar may be used, the ends of which must be
turned perfectly cylindrical, and the telescope be removed from one
end of the bar or line to the other end for observation; or each end
of the bar or tube may be provided with a disc, against each of
which a telescope may be affixed, the one stationary, the other
moveable from a centre, and the circle graduated, or both moveable.
For portability, the bar or platform, or any line which is used,
may be jointed. This jointed bar is applicable to double telescopes
of
every description. Or when a motion in the centre is required, two
or three bars of unequal lengths may be employed. See Figs. 2, 3,
4, and 5, A, B, C, with parallel and horizontal adjustments D.
Also, when a stand cannot be used, a telescope fixed in a graduated
tube moving in another tube, or on a line of any description, is
used, by sliding the telescope from the eye.
To prevent injury to the glasses of these telescopes and every
description of telescope, varnish the inside or outside of the tubes
with a solution of india rubber, gutta percha, or shellac; apply a
layer of paper and leather, or any other material that will prevent
the deposit of a vapour on the glasses.

page_text: SPECIFICATION in pursuance of the conditions of the Letters
Patent, filed by the said Isaac Davis in the Great Seal Patent
Office on the 26th July 1853.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I,
ISAAC DAVIS, of 119, High Holborn, in the County of Middlesex,
Optician, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-sixth day of January,
in the year of our Lord One thousand eight hundred and fifty-
three, in the sixteenth year of Her reign, did, for Herself, Her
heirs and successors, give and grant unto me, the said Isaac Davis,
Her special licence that I, the said Isaac Davis, my executors,
administrators, and assigns, or such others as I, the said Isaac
Davis, my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times
thereafter during the term therein expressed, should and lawfully
might make, use, exercise, and vend, within the United Kingdom.
of Great Britain and Ireland, the Channel Islands, and Isle of
Man, an Invention for "IMPROVEMENTS IN OPTICAL AND MATHEMATICAL
INSTRUMENTS," upon the condition (amongst others) that I, the
said Isaac Davis, by an instrument in writing under my hand
and seal, should particularly describe and ascertain the nature
of the said Invention, and in what manner the same was to
be performed, and cause the same to be filed in the Great Seal
Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Isaac Davis, do hereby
declare the nature of my said Invention, and in what manner
the same is to be performed, to be particularly described and
ascertained in and by the following statement and the Drawings
hereunto annexed (that is to say):
My Invention consists in a new application of the telescope or
telescopes for determining distances, and registering the state of the
atmosphere, by the increase or decrease of the field of view, which

page_text: increase and decrease is formed into a table or index to indicate and
fortel the changes in the atmosphere. I use telescopes of two feet
focal length, or thereabouts, and place cross wires or other suitable
divisions in them horizontally and vertically. Two of these telescopes
are placed parallel on a theodolite or other suitable stand. The base,
cylinder, line, or platform A, Figure 1, to which the telescopes are
attached, may be used vertically or horizontally. One of the
telescopes is attached by means of a square box, so as to slide easily
along, and is kept in position by a support travelling on the stand,
or by any other suitable means; the other is mounted on a circle,
or a portion of a divided circle, or a micrometer screw with a
divided circle. The part A, is divided into a graduated scale.
Observe any object at a convenient distance that shall cut the left
vertical wire or division in the telescope; slide the telescope along
the cylinder till it appears to touch the right-hand vertical wire;
the space travelled over by the telescope will indicate the distance
of terrestrial objects. To form a table of the state of the atmosphere,
two telescopes are generally necessary. The second telescope had
better be placed on the point or place where the first was removed
from; but it is not absolutely necessary. The separation of the two
telescopes may be about two feet apart. Both telescopes are to be
directed to an object, and the vertical wire on the centre of each
telescope made to coincide with the object. The divided circle may
be set at zero by any suitable means, and the variations of the object
observed and registered by the divided circle; which registrations
will serve as a table to indicate the state of the atmosphere.
Figure 2, is intended to ascertain the value between the wires on
the telescopes to graduate the cylinder or tubes of the different forms
of instruments used, and also is used to determine distances. Take
one or more lengths of tube, or any other suitable material which is
not likely to alter in dimensions, which may be graduated and pro-
vided with two signs or objects B, C, (one or both moveable,) and
placed at a distance from the observer, who is provided with a
telescope fixed on a stand, or a theodolite, or any other instrument
having a telescope attached thereto, and an assistant will move the

page_text: signs or objects on the graduated line, Figure 2, till each sign
appears to touch the wires or divisions. These signs will have to be
moved outwards or inwards, that depending on the distance of the
assistant from the observer. To ascertain the value of these wires
is as follows: At a short distance, observe carefully the separation
of the two signs that coincides with the separation of two wires or
divisions in the telescopes intended to be used; measure the distance
with glass rods or any other suitable means, as the apparent magni--
tude of bodies increase or decrease very nearly with their distances.
inversely, or that at twice the distance they appear twice as sinall,.
and at half the distance they appear twice as large; at twice the
distance the graduated line Figure 2, will have to be moved twice
as much, at half the distance half as much. When one distance is.
known, all other distances can be found by calculation and engraved
on the instruments. Figure 3, This telescope is used vertically on
a perfect cylinder, having a vertical joint near its base, or rougli
drawn sliding graduated tubes, or other suitable means. By fixing
to the telescope a graduated spirit level with a vertical joint and
tangent screw, the tubes A are drawn out, and the instrument for
observation set by the moveable vertical joint near the base, the
object touching the under horizontal wire. The spirit level is set
at zero. The tubes are pushed downwards till the object appears to
touch the upper horizontal wire. If the level remains at zero, the
graduated tubes show the distance travelled over between the wires.
If the bubble of the level be not at zero, it must be made so by the
tangent screw, which moves the telescope independent of the level.
When the level and space travelled over coincide with the upper
horizontal wire, the observation is complete. Figure 4, is a vertical
and horizontal instrument, and may be used horizontally or ver-
tically with one or two telescopes. If used with two telescopes,
only two cross wires on each are necessary,-one horizontal, and
one vertical; but if used with one telescope, three wires or more
divisions are necessary. The telescope or telescopes may be used on
a perfect cylinder or graduated tubes, or other suitable means (A).
On the telescope a spirit level is fixed, more exposed than in ordinary

page_text: levels. An extra horizontal motion (D) is placed next to the
tubes, cylinder, or line, and the level adjusted as before described in
Figure 3. Instead of the spirit level fixed on the telescope, a square
provided with a dial plate and index (Figure 5), with a weight at
one end, may be used. To increase the field of view of binoculars,
I prefer a hinged bar (Figure 6), instead of the sliding tubes before
described. The moveable signs or objects herein-before described are
applicable to stereoscopic views, by increasing or decreasing the
field of view so as to suit each person's sight. To prevent injury
by the action of the atmosphere to these and all other description
of telescopes and optical instruments, I line the interior with
leather, india-rubber, and shellac, dissolved in spirits of wine or
any other non-conducting and absorbing substance.
Having now described my Invention, I do not confine myself
to the precise details herein expressed, so long as the principle of
my Invention be retained.
In witness whereof, I, the said Isaac Davis, have hereunto set
my hand and seal, this Twenty-sixth day of July, One
thousand eight hundred and fifty-three.
ISAAC DAVIS. (L.S.)