CERTAIN IMPROVEMENTS IN OPTICAL INSTRUMENTS OR APPARATUS
Year: 1814

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
FRANCIS HAMILTON, of Asylum Buildings, Westminster Road, in the Parish
of Saint Mary, Lambeth, in the County of Surrey, Engineer, send greeting.
. WHEREAS His present Majesty King George the Third, in and by His
Letiers Patent under the Great Seal of Great Britain, bearing. date at West-
minster, the Twelth day of February last, for Himself, His heirs, and
successors, did give and grant unto me, the said William Francis Hamilton,
His spécial licence, full power, sole privilege and authority, that 1, the said
William Francis Hamilton, my executors, administrators, and assigns, and
every of them, by myself and themselves, or by my and their deputy or
deputies, servants or agents, or such others as I, the said William Francis
Hamilton, 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, in England and Wales, and the Town of Berwick-upon-Tweed,
and also in His Majesty's Colonies and Plantations abroad, my Invention of
"CERTAIN IMPROVEMENTS IN OPTICAL INSTRUMENTS OR APPARATUS," in which said
Letters Patent there is contained a proviso, obliging me, the said William
Francis Hamilton, 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 Majesty's High Court of Chancery within two calendar months nexi
and immediately after the date of the said recited Letters Patent, as in and
by the same, reference being thereunto had, will more fully appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, 1, the said
William Francis Hamilton, do hereby declare that the nature of my said
Invention, and the manner of performing the same, are particularly described
and ascertained as follows, that is to say:
Firstly, in the improvements delineated and set forth in Figure 1, hereunto
annexed, the letter a denotes an object glass or single lens, having its focus of
parallel rays positive, and the letter b denotes a meniscus or concavo convex
lens, having its focus of parallel rays negative or vertual, and the said lenses
are so disposed that they have one common axis, the concave surface of the
meniscus being nearest to a, and the convex surface of the same being silvered;
and I do admit the rays of light from remote objects on the side or region c
to fall upon and pass the lens a, and converge of course towards b. And
further, I do intercept the said converging rays by the meniscus b, which for
that purpose I do place at the distance from a, by preference, of about one-
fifth or sixth part of the focal length of the said lens a. And, moreover, I do
make the curvatures of the surfaces of the meniscus a such as that the
aberrations from sphericity, and from the unequal or chromatic refraction of
light produced by the lens a. shall be corrected or nearly so, as to practise by
the contrary refraction effected in passing to the remoter or silvered surface
of b, and back again towards the common axis from the last-mentioned lens
or glass, at or near which axis a correct image will be formed. And I do
view the said image by an eye piece of any of the usual constructions,
containing a small inclined speculum, or otherwise, by what has been called
the direct view, in large reflecting telescopes, wherein the focal image is
thrown out of the axis by inclining the reflection, as may be done with
the meniscus in my said improvement. And I do further declare, that my
said improvement is particularly adapted to astronomical uses, and that the
considerable focal length of the lens « renders it convenient for bisection as a
micromater. And lastly, as to the said Figure 1. that the lines which are drawn
in contact with the capital letter A, would, if continued, form an angle denoting
the angle of deflection produced in the incident ray by the refraction of the
lens a, and that the lines which are drawn in contact with the capital letter B
would, if continued, form an angle denoting the angle of deviation produced
in the incident ray by the contrary refration of the meniscus b, and that the
lines which are drawn in contact with the capital letter C would, if continued,
form an angle denoting the angle made by the ray after reflection, and the ray
which impinged at the point of reflection. f, 1, 1, 1, shews the space over
which the false lights are diffused, which from its great extent renders them
of no consequence. And I do further declare, that if both lenses be. made of
glass of a medium or mean refractive power and of the same kind of glass,

page_text: (which last, in order to avoid the tertiary chromatic refraction, is desirable.)
the single object lens may be made plano-convex, having the convex side out-
wards, and that whatever may be the radius of curvature of the said convex
surface, the concave surface of the meniscus must have its radius equal to
three-ninth parts of the said first-mentioned radius, and the convex surface of
the meniscus must have its radius equal to five-ninth parts of the said first-
mentioned radius; or in case the lens a be a double convex, the last-mentioned
numbers must each be diminished to one half, and that such and the said
proportions will in practice afford an improvement, by which the instrument
will be correct or very nearly so. And farther, that I have not considered it
to be needful to explain the general principles of optical theory upon which
the improvements hercin set forth are founded and established, because the
said general principles are well known to opticians, who will easily apply the
sane unto the said improvements.
And, secondly, in the improvement delineated and set forth in Figure 2,
hereunto annexed, the letter A denotes an achromatic object glass, to receive
parallel rays; and B denotes a second achromatic object glass in a fixed position
to receive converging rays; and C denotes an amplifying lens; and D, a concave
eye-glass, both which last are so adapted to each other with regard to figure
and materials, as to correct the aberrations of sphericity and colour in the eye
piece; and the letter a denotes the focal point of the first object glass A,
taken singly, and the letter b denotes the focal point of parallel rays, after
having passed through the lenses A and B, as combined in the Figure.
In witness whereof, I have hereunto set my hand and seal, the Twelfth
day of April, in the year of our Lord One thousand eight hundred
and fourteen.
WILLIAM FRANCIS HAMILTON. (L.S.)
AND BE IT REMEMBERED, that on the same Twelfth day of April, in
the year above mentioned, the aforesaid William Francis Hamilton came
before our Lord the King in His Chancery, and acknowledged the Specifica-
tion aforesaid, and all and every thing therein contained, in form above written,
And also the Specification aforesaid was stamped according to the tenor of
the Statute in that case made and provided.
Inrolled the same Twelfth day of April, in the year above written