IMPROVEMENTS IN ACHROMATIC OBJECT GLASSES FOR MICROSCOPES
Year: 1872

page_text: LETTERS PÅ ENT to Francis Herbert Wenham, of Padnal Hall,
Chadwell, in the County of Essex, Engineer, for the Invention of
PROVISIONAL SPECIFICATION left by the said Francis Herbert
Wenham at the Office of the Commissioners of Patents, with
his Petition, on the 30th May 1872.
I, FRANCIS Herbert Wenhaм, of Padnal Hall, Chadwell, in the
County of Essex, Engineer, do hereby declare the nature of my said
Invention for "IMPROVEMENTS IN ACHROMATIC OBJECT GLASSES FOR MICROSCOPES,"
to be as follows:-
This Invention consists of an object glass composed of a series of
lenses set in three separate cells. The back lens is a simple double
convex, the middle is a triple achromatic, consisting of a double con-
cave lens of dense flint glass of high dispersive power between two lenses
of crown glass, the foremost of which is a plano-convex, and the posterior
a double convex; these lenses are cemented together with Canada balsam

page_text: at the contact surfaces, which are of similar radii. The front lens of
this object glass is a single lens made of a thickness suitable for cor-
recting spherical aberration, and has the usual arrangement for separating
it more or less from the others to correct the errors caused by the thick-
ness of the covering glass of objects.
Object glasses have been made with a triple back, a double middle,
and a triple front lens, these terms meaning that each has its own
correcting concave flint glass lens, but in some cases a single front lens
has been employed.
The new feature in this Invention is that one concave lens of dense
flint glass is made to correct four lenses of crown glass, so that achro-
matism and correction are obtained in the combined series.
By this Invention superior object glasses may be produced at a cheaper
rate than heretofore.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Francis Herbert Wenham in the Great Seal Patent
Office on the 22nd November 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FRANCIS
HERBERT WENHAM, of Padnal Hall, Chadwell, in the County of Essex,
Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirtieth day of May, in the year of
our Lord One thousand eight hundred and seventy-two, in the thirty-fifth
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said Francis Herbert Wenham, Her special license
that I, the said Francis Herbert Wenham, my executors, administrators,
and assigns, or such others as I, the said Francis Herbert Wenham,
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 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 ACHROMATIC OBJECT GLASSES FOR MICROSCOPES," upon the condition
(amongst others) that I, the said Francis Herbert Wenham, my exe-

page_text: cutors or administrators, 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 Francis Herbert Wenham, 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, reference being had to the accom-
panying Drawings, and to the letters and figures marked thereon, that
is to say :-
My said Invention consists of an object glass composed of a series of
lenses set in three separate cells. The back lens is a simple double or
plano-convex, the middle is a triple achromatic, consisting of a double
concave lens of dense flint glass of high dispersive power between two
lenses of crown glass, the foremost of which is by preference a plano-
convex, and the posterior a double convex; these lenses are cemented
together with Canada balsam at the cont surfaces which are of
similar radii. The front lens of this object glass is a single lens made
of a thickness suitable for correcting spherical aberration, and has the
usual arrangement for separating it more or less from the others to
correct the errors caused by the thickness of the covering glass of objects.
Object glasses have been made with a triple back, a double middle,
and a triple front lens, these terms meaning that each has its own
correcting concave flint glass lens, but in some cases a single front lens
has been employed.
The new feature in this Invention is that one concave lens of dense
flint glass is made to correct four lenses of crown glass, so that achro-
matism and correction are obtained in the combined series.
By this Invention superior object glasses may be produced at a cheaper
rate than heretofore.
The accompanying Drawing represents the three separate lenses of
my improved object glass for microscopes. The back lens A is a plano-
convex or double convex of crown glass; the middle lens B is a triple
achromatic, consisting of the double concave lens a of dense flint glass

page_text: situate between the two lenses b and c of crown glass, the foremost one c
being either a plano-convex (as shewn in the Drawing), or a double
convex, or a concavo-convex, whilst the posterior one 6 is a double
convex; C is the front lens of the object glass composed of crown glass
of the well-known construction.
Having now described and particularly ascertained the nature of my
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion that what I consider to
be novel and original, and therefore claim as the Invention secured to
me by the herein-before in part recited Letters Patent is, the combination
of a double concave flint glass lens between two crown glass lenses,
such a triple combination forming the middle lens situated between a
separate front and back lens, the series constituting the object glass of
a microscope, substantially as herein-before described and illustrated
by the Drawing hereunto annexed.
In witness whereof, I, the said Francis Herbert Wenham have
to this my Specification set my hand and seal, the Twenty-first
day of November One thousand eight hundred and seventy-
two.
FRANCIS HERBERT WENHAM.
(L.S.)