AN INSTRUMENT WHEREBY ANY PERSON MAY DRAW IN PERSPECTIVE, OR MAY COPY OR REDUCE ANY PRINT OR DRAWING
Year: 1806

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
HYDE WOLLASTON, of the Parish of Saint Mary-le-bone, in the County of
Middlesex, Gentleman, send greeting.
WHEREAS His present most Excellent Majesty King George the Third,
in and by His Letters Patent under His Great Seal of the United Kingdom
of Great Britain and Ireland, bearing date at Westminster, the Fourth day of
December, in the forty-seventh year of His reign, for Himself, His heirs and
successors, did give and grant unto me, the said William Hyde Wollaston, my
executors, administrators, and assigns, His especial license, full power, sole
privilege and authority, that I, the said William Hyde Wollaston, my
executors, administrators, and assigns, and every of them, by myself and them-
selves, or by my and their deputy or deputies, servants or agents, or such
others as I, the said William Hyde Wollaston, my executors, administrators,
or assigns, should at any time agree with, and no others, from time to time
and at all times thereafter during the term of years therein expressed, should
and lawfully might make, use, exercise, and vend, within that part of His said
Majesty's United Kingdom called England, His Dominion of Wales, and the
Town of Berwick-upon-Tweed, my Invention of "AN INSTRUMENT WHEREBY
ANY PERSON MAY DRAW IN PERSPECTIVE, OR MAY COPY OR REDUCE ANY PRINT OR
DRAWING;" in which said Letters Patent there is contained a proviso obliging
me, the said William Hyde Wollaston, by an instrument in writing under my
hand and seal, particularly to describe and ascertain the nature of my said
Invention, and in what manner the same is to be performed, and to cause the
same to be inrolled in His said Majesty's High Court of Chancery within one.

page_text: calendar month next and immediately after the date of the said in part recited
Letters Patent, as in and by the same, relation being thereunto had, may more
fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
William Hyde Wollaston, do hereby declare that my said Invention is
described in manner following, that is to say :-
My said instrument consists principally of two reflecting surfaces, so placed
with regard to each other as that one (which I will call the first) of the said
surfaces shall be wholly or in part interposed between the eye of the artist and
the paper or other material upon which the delineation of any object or view,
or the copy or reduction of any sketch, print, or drawing shall be intended to
be made; and the said reflecting surface shall be so inclined toward the other
(which I will call the second) reflecting surface, that objects reflected by that
second reflector may also be again reflected by the first, and may by that
means be rendered visible to the eye after two reflections, when the sight is
.directed towards the said paper or other material; and in order that the said
paper or other material may be seen by the same eye, as well as the doubly
reflected object, I make the said first-mentioned reflector of such materials as
shall permit the said paper or other material to be seen through the same; or
otherwise I make the said first-mentioned reflector of materials not capable of
transmitting the light, and in this case I do interpose the same in part only
between the eye and the said paper or other material. In the former con-
struction the first reflector may be a piece of plain and unsilvered glass, which
is capable of exhibiting the image of a considerably luminous object by
reflection, at the same time that a piece of white paper or other surface may
be seen through the glass, and the image of that object may be traced upon
the said paper or other surface; but in case the object be less bright, it may
not be seen by reflection from clear white glass distinctly enough to be
delineated, and in this case glass that is blue, or of any other dark colour, will
be preferable, but it is in general better to use for the first reflector a glass
partly silvered, and to allow the paper to be seen through an opening in the
silvering or past the edges of the sanic by one portion of the eye, while the
doubly reflected object is seen in the silvering by the other portion of the
same eye.
And I do further declare that my said instrument might also be made s
with surfaces which act by what opticians call prismatic reflection. but that I
do not give the preference to surfaces of this last description, because when
the reflected object is much illuminated it may thus be made too bright to
allow the paper and pencil to be seen distinctly. The most convenient position

page_text: in which the said reflecting surfaces can be placed with regard to each other is
such that the rays proceeding from the object, and falling on the first mirror (which
are known to opticians by the denomination of 'the incident rays) shall each
severally be at right angles to that portion of the same ray which after reflection
proceeds to the eye (and is known by the denomination of the emergent ray),
because in these circumstances the instrument will be adapted to drawing
upon a horizontal surface. And in order that the said incident and emergent
rays may be at right angles to each other, it is requisite that the reflecting
surfaces should be inclined to each other at an angle of forty-five degrees), as is
shewn in Figure 1, hereunto annexed, or at an angle of one hundred and
thirty-five degrees (which is the supplement of forty-five degrees), as is shewn
in Figure 2. a, b, in such Figure, is the section of a reflector, partly trans-
parent and partly silvered. m, n, is the surface of the same glass, and othe
part silvered. c, d, in each Figure is the section of a glass wholly silvered.
When prismatic reflection is employed, the angle of the reflecting surfaces to
produce a like effect must be one hundred and thirty-five degrees, as in
Figure 3, which represents the section of a solid prismatic piece of glass, in
which both reflections are made, and the reflecting surfaces are a, b, and b, c.
The angle at bis 185 degrees, and the angle at d 90 degrees, and the angles
at a and c may be each 67 degrees, but need not necessarily be equal. In
each of these Figures e is the place of the eye, to which a ray h, g, after being
reflected at g and f, passes on in a direction f, e, at right angles to h, g. Tho
glasses or other suitable reflecting surfaces herein-before described, when
properly mounted, and supported at a convenient distance from the paper or
other material upon which the said delineation, copy, or reduction is to be
made, do, together with the necessary framing (which every competent work-
man may easily make of a variety of forms without further instruction), con-
stitute the whole of my said instrument adapted to the use of persons who
can with facility see both near and distant objects; but for persons who are
short-sighted I place a suitable concave glass before the distant object, so as to
receive and transmit the incident rays; and for long-sighted persons I place a
suitable convex glass between the eye and the said paper or other material.
Figure 4 represents the section of a pair of reflectors at an angle of forty-
five degrees, to be mounted in a frame which carries one convex glass i, k,
and another concave glass m, n, which turn upon the same hinge at l, so that
either of them may be turned into its place for use. In the position here
given the convex glass is supposed to be employed, and the line o, p, represents
aray by which the paper and pencil are seen at the same time that the object
s seen by rays reflected through h, g, f, e, which render the same visible in the

page_text: direction e, f. The said convex and concave glasses may conveniently be
made of the focal length of twelve inches, and the instrument must then be
supported at the distance of twelve inches from the paper.
In witness whereof, I, the said William Hyde Wollaston, have hereunto
set my hand and seal, this Third day of January, in the year of our
Lord One thousand eight hundred and seven..