IMPROVEMENTS IN FLUID LENSES
Year: 1869

page_text: COMPLETE SPECIFICATION filed by William Brookes at the Office of
the Commissioners. of Patents, with his Petition and Declaration,
on the 4th December 1869, pursuant to the 9th Section of the
Patent Law Amendment Act, 1852.
TO ALL TO WHOM, THESE, PRESENTS SHALL COME, I, WILLIAM
BROOKES, of 62, Chancery Lane,. in the County of Middlesex, Civil
Engineer and Patent Agent,. do. hereby declare the nature of the said
Invention for "IMPROVEMENTS IN FLUID LENSES," (that the same has been
communicated to me from abroad by David Acheson Woodward, of the
City of Baltimore, in the State of Maryland, in the United States of
America, Photographer,) and in what manner the same is. to. be.
performed, to be particularly described and ascertained in and by the.
following statement thereof, reference being had to the accompanying
Drawings through letters of reference marked thereon, that is to.
say :-
Figure 1 represents a lens of the plano-convex form constructed
according to the Invention; Figure 2 is a perspective view of the same;
Figure 3 is a double convex lens; Figure 4 represents the manner of
combining two cells for making an achromatic lens; Figures 1, 3, and 4

page_text: being transverse sectional views taken through the centre of these lens.
Similar letters of reference indicate corresponding parts in the several
Figures.
The nature of the Invention consists in bending circular discs of
polished, flattened, or plate glass to any required curvature either
spherical or parabolical, and afterwards cementing and firmly securing
them together by means of rings or bands of metal or other suitable
material, thus forming cells for holding fluids whereby a fluid lens or any
combination of fluid lenses may be made of any required focus and of a
size much larger than can be made of solid glass, and by means of the
spherical or parabolically curved glasses the metallic rebated rings and
system of cementing which are employed a combination of cells may
be formed for holding fluids of different indices of refraction, thus
forming a fluid lens which will overcome both spherical and chromatic
aberation in its own construction, and also whereby reflectors can be
made of any of the precise and exact curvature herein-before mentioned,
the shells of glass being silvered by any method that can be used for the
silvering of mirrors. The reflectors made by this process being not
anly exact in curvature can also be made of any size limited by the
dimentions of the flat plates or shects of glass that can be obtained
for the purpose.
To enable others to make and use this Invention I will proceed to
describe its construction and operation with reference to the Drawings.
A hollow or disc-like mould of soapstone or other suitable material is
prepared of the precise mathematical curve required. The glass is cut
in a circular form of the required size and placed on the mould, when it
is exposed to a heat just sufficient to cause the glass to bend by its own
weight and conform itself to the bottom of said concave mould. If this
operation is properly conducted and not too much heat employed the
polished surface of the glass shell thus formed will not be in the least
injured.
To combine two or more of these glasses or shells a metallic ring A
is used forming on its inner side a rebate of annular shape, in which one
of the glasses is imbedded in suitable cement, and the shell or glass that
is to form the other side of the cell is then laid on and the cement well
packed in the rebate, and around the edges of the glasses. The flat
ring Cis then screwed on or bolted down upon the cement holding it
firmly and compactly in the rebate. An opening or aperture O is

page_text: formed through the metallic ring, cement, and edges of the curved glass
or glasses for the introduction of the fluid and is provided with a screw
plug S to retain it,
To provide for the expansion of the fluids in the cell or cells one
or more air chambers may be formed above either or both of the
openings O, O'. The fluid or liquid used may be a saturated solution
of alum, chloride of sodium or calcium, or concentrated glycerine, and
doubtless there are many others equally suitable; I do not therefore
restrict myself to any in particular. In charging the cells of the
achromatic lens the plano-concave is first filled with the saturated solu-
tion and then the other with the same solution diluted. The amount or
degree of dilution required will vary with the various curvatures of the
plates, and is best determined by allowing the light to pass through and
diluting until the chromatic aberations corrected, which is known by
the disappearing of the colored fringe around the reflection on the wall
or other object. Any of the above-mentioned fluids dilute with water or
alcohol. The cement used must be adapted to resist the action of the
particular fluid to be used. For any of the above red lead, white lead,
putty, or any oleaginous paste answers well. Gutta percha or india-
rubber may be used, but for bi-sulphuret of carbon or the like which mix
freely with oil, an earthy base, such as kaolin mixed with gum tragacanth,
will answer well for the cement; I do not therefore restrict myself to any
in particular.
In making an achromatic lens two rebated rings A, d, are used con-
nected by a cylinder H, as represented in Figure 4. In the rebate of
the ring A is cement a circular flat plate glass and a curved glass or
shell which form a plano-convex cell K, or two curved glasses may be
used forming a double convex cell, and in the rebate of the ring a is
secured another curved glass L with its concave side outwards, thus
forming with the flat plate glass N another cell of the plano-convex
form M to be filled through an opening O' in the cylinder H with a
fluid of a high refracting index (the bi-sulphuret of carbon for instance);
whilst the cell K is filled with a fluid of a lower refracting index, as
hercin-before described. The refracting power of the two fluids in their
respective cells being properly adjusted in relation to each other by
dilution or otherwise are made to correct each other for chromatic
aberation in the same manner that a solid bi-convex lens of crown glass

page_text: and a solid bi-concave lens of flint glass correct each other in the ordinary
way.
Doubtless curved glasses could be made by some other method than
that herein described, either by blowing, pressing, or grinding and
polishing, but the process herein described by bending is practically by
far the cheapest and the best.
Fluid lenses have been made by cementing together two watch glasses
for experimental purposes; also attempts have been made to use
refracting fluids in combination with a lens of crown or solid glass in
order to correct chromatic aberation; also bending glass by its own
weight when highly heated it not new. I therefore do not claim either
of these per se; but what I claim as the Invention and desire to secure
by Letters Patent is,―
First. The method herein described of bending discs of glass so as
to produce a convex or concave lens of spheroidal, parabolic, or hyperbolic
profile for the purpose set forth.
Second. The use of two or more pieces of plate or flattened glass bent
to the required curve or profile as herein specified in combination with
the cement and rings, or their equivalents, for holding them together,
substantially as set forth.
Third. Combining with three or more glasses formed into cells as
described, fluids of different indices of refraction that will correct
chromatic aberation, substantially as described.
Fourth. The method herein described of bending discs of glass so as
to produce a convex or concave reflector of spheroidal, parabolic, or
hyperbolic profile.
In witness whereof, I, the said William Brookes, have hereunto
set my hand and seal, this Fourth day of December, in the
year of our Lord One thousand eight hundred and sixty-nine.