AN IMPROVEMENT IN SPECTACL ESBY THE APPLICATION OF CONCAVO-CONVEX GLASSES TO THEM
Year: 1804

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
HYDE WOLLASTON, of Buckingham Street, Fitzroy Square, in the County of
Middlesex, Gentleman, send greeting.
WHEREAS His present Majesty King George the Third, by His Letters
Patent under the Great Seal of Great Britain, bearing date at Westminster,
the Ninth day of February, in the forty-fourth year of His reign, did give
and grant unto me, the said William Hyde Wollaston, my exors, admors, and
assigns, His especial licence, full power, sole privilege and authority, that I,
the said William Hyde Wollaston, my exors, adññiors, and assigns, during
the term of years therein expressed, should and lawfully might make, use,
exercise, and vend, within England, His Dominion of Wales, and Town of
Berwick-upon-Tweed, my new Invention of "AN IMPROVEMENT IN SPECTACL ESBY
THE APPLICATION OF CONCAVO-CONVEX GLASSES TO THEM;" in which Letters Patent
there is contained a provisoe obliging me, the said William Hyde Wollaston,
under my hand and seal, to cause a particular description of the nature
of my said Invention, and in what manner the same is to be performed, to
be inrolled in His Majesty's High Court of Chancery within one calendar
month next immediately after the date of the said 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 provisoe, I, the said
William Hyde Wollaston, do hereby particularly describe and ascertain the
nature of my said Invention, and in what manner the same is to be performed,
as follows, that is to say:
The object of my said Invention is to remedy the following defect which has
been observed in spectacles heretofore in use, viz, that no objects appear
distinct through them but such as are seen through the centers of the glasses,

page_text: or nearly so, but are indistinct in proportion to the distance of the part of the
glass through which they are seen from the center, whether sideways or
upwards or downwards, that is to say, the indistinctness is greater in propor-
tion as the rays of light passing from an object to the eye pass more obliquely
through the glass, as is represented by the lines E, O, in Figures 1 and 2, in
FIG.1.
A
FIG. 2
0
which E is the place of the eye, and A, O, in each is a
section of a spectacle glass of the common defective
construction. I have found that the defect above men-
tioned may be remedied by means unnoticed by the
best practical opticians, and contrary to the opinion of
the most celebrated writers on optical subjects. Having
observed that the portion of any glass employed in any
⚫ one position of the eye is small, I perceived that by
making the substance of a glass curved in the manner
of a hollow globe, each portion of it might be situated
nearly at right angles to the direction of the sight, and
would thereby render lateral objects distinct, without impairing the distinctness
at the center.
E
FIG. 3.
My Invention therefore consists in the application of this principle to
spectacles, and my method of doing so is by having the glasses thereof of a
form not heretofore used for that purpose; and the form of the said glasses is
such that the outer surface of each glass, or that which is farthest from the
eye, is spherically convex, and the inner surface of the same glass, or that
which is nearest to the eye, is spherically concave. A section of this form of
glass, as represented by the Drawing, Fig. 3, is adapted
for a short-sighted person, having the interior and
concave surface of each glass more curved than the
exterior and convex surface of the same glass, by which the rays of light
passing through the same are diverged, and the degree of curvature of the
interior and concave surface is to be increased in proportion as the person to
use the glasses is the more short sighted. For long-sighted persons the form
of each glass must be such as to have the exterior and convex surface thereof
more curved than the interior and concave surface of the same glass, as is
represented by a section of the said form of glass in the Drawing, Fig. 4, by
FIG. 4
which the rays of light passing thro' the
same are converged, and the degree of
curvature of the exterior and convex
surface of the glass is to be increased in

page_text: preparing such glasses, and of proportioning their curvatures so as to give them
any power of magnifying or diminishing that may be required, and to suit the
different sights of long and short sighted persons, are too well known to
persons skilled in optics to need any description.
In witness whereof, I have hereunto set my hand and seal, the Seventh
day of March, in the year of our Lord One thousand eight hundred
and four.