IMPROVEMENTS IN THE MANUFACTURE OF LENSES FOR PHOTOGRAPHIC CAMERAS AND VARIOUS OPTICAL INSTRUMENTS
Year: 1867

page_text: LETTERS PATENT to Thomas Ross, of Featherstone Buildings, in the
County of Middlesex, Optician, for the Invention of "IMPROVEMENTS IN
THE MANUFACTURE OF LENSES FOR PHOTOGRAPHIC CAMERAS AND VARIOUS OPTICAL
INSTRUMENTS."
Sealed the 19th July 1867, and dated the 23rd January 1867.
PROVISIONAL SPECIFICATION left by the said Thomas Ross at the Office
of the Commissioners of Patents, with his Petition, on the 23rd January
1867.
I, THOMAS Ross, of Featherstone Buildings, in the County of Middlesex,
Optician, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN THE MANUFACTURE OF LENSES FOR PHOTOGRAPHIC CAMERAS AND VARIOUS
OPTICAL INSTRUMENTS," to be as follows:-
The Invention has for its object improvements in the manufacture of
lenses for photographic cameras and various optical instruments. Heretofore,
in order to obtain achromatic lenses for various instruments it has been
customary to construct the convex glass of crown glass and the concave
glass of flint glass.
Now my Invention consists in the employment of different descriptions or
qualities of flint glass or of crown glass for both the convex and concave
glasses; the glass employed for the convex being that known as light flint or
light crown glass, and having a low refractive and dispersive power, whilst the
glass used for the concave is of the description known as heavy or dense flint
glass, or heavy or dense crown glass, and having a high refractive and dis-

page_text: persive power, whereby the different degrees of refrangibility of the two
descriptions or qualities of crown glass, or of the two descriptions or qualities
of flint glass, counteract or neutralize each other.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Ross in the Great Seal Patent Office on the
23rd July 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
Ross, of Featherstone Buildings, in the County of Middlesex, Optician, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-third day of January, in the year of our Lord
One thousand eight hundred and sixty-seven, in the thirtieth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said Thomas Ross, Her special licence that I, the said Thomas Ross, my
executors, administrators, and assigns, or such others as I, the said Thomas
Ross, 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
THE MANUFACTURE OF LENSES FOR PHOTOGRAPHIC CAMERAS AND VARIOUS OPTICAL
INSTRUMENTS," upon the condition (amongst others) that I, the said Thomas
Ross, my executors or administrators, by an instrument in writing under
my, or their, or one of their hands and seals, 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 Thomas Ross, do hereby declare
the nature of the said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement thereof, that is to say :—
The Invention has for its object improvements in the manufacture of lenses
for photographic cameras and various optical instruments. Heretofore, in
order to obtain achromatic lenses for various instruments it has been cus-
tomary to construct the convex glass of crown glass and the concave glass of
flint glass.

page_text: Now my Invention consists in the employment of different descriptions or
qualities of flint glass or of crown glass for both the convex and concave
glasses; the glass employed for the convex being that known as light flint or
light crown glass, and having a low refractive and dispersive power, whilst the
glass used for the concave is of the description known as heavy or dense flint
glass, or heavy or dense crown glass, and having a high refractive and dis-
persive power, whereby the different degrees of refrangibility of the two
descriptions or qualities of crown glass, or of the two descriptions or qualities
of flint glass, counteract or neutralize each other.
I have not thought it necessary to enter into a description of the different
degrees of density or specific gravity, or of the forms which may be given to
the convex and concave glasses when both of such glasses are according to my
Invention constructed of flint glass or of crown glass, as such will be dependent
upon each other, and upon the particular purpose to which the lens is to be
applied, and requires no further information to enable an optician to construct
lenses according to my Invention, as he will readily understand that the degree
of convexity or of concavity for the convex and concave glasses of lenses will
depend upon and be regulated by the density, and consequently by the
different degrees of refractive and dispersive power possessed by the glass
employed.
Having thus described the nature of my Invention, and the mode in which
the same may be carried into effect, I would have it understood that what I
claim is, the manufacture of lenses for photographic cameras and various
optical instruments in which the convex and concave glasses are constructed
of two different qualities or densities of either crown glass or of flint glass, as
herein described.
In witness whereof, I, the said Thomas Ross, have hereunto set my
hand and seal, this Eighteenth day of July, in the year of our Lord
One thousand eight hundred and sixty-seven.
Witness,
B. J. B. MILLS,
Patent Agent,
35, Southampton Buildings,
Chancery Lane.
THOMAS ROSS. (L.S.)