AN IMPROVEMENT IN OBJECT GLASSES FOR MICROSCOPES
Year: 1878

page_text: LETTERS PATENT to Alfred Vincent Newton, of the Office for Patents, 66,
Chancery Lane, in the County of Middlesex, Mechanical Draughtsman, for
the Invention of "AN IMPROVEMENT IN OBJECT GLASSES FOR MICROSCOPES."
A communication from abroad by Ernst Gundlach and John Jacob Bausch,
of Rochester, in the State of New York, and Henry Lomb, of Brooklyn, in
the State of New York, United States of America.
ealed the 18th April 1878, and dated the 13th February 1878.
PROVISIONAL SPECIFICATION left by the said Alfred Vincent Newton at
the Office of the Commissioners of Patents on the 13th February 1878.
ALFRED VINCENT NEWTON, of the Office for Patents, 66, Chancery Lane, in the
County of Middlesex, Mechanical Draughtsman. "AN IMPROVEMENT IN OBJECT
GLASSES FOR MICROSCOPES." [A communication from abroad by Ernst Gundlach
and John Jacob Bausch, of Rochester, in the State of New York, and Henry Lomb,
of Brooklyn, in the State of New York, United States of America.]
The object of this Invention is to provide a more effectual means than those
heretofore employed for the adjustment of the object glasses of microscopes to suit
the varying thicknesses of the glass covers of object slides.
The performance of object glasses for microscopes constructed on the plan hitherto
adopted can be perfect only for covers of one thickness, while for covers of all
other degrees of thickness the performance is deteriorated, and this obtains to an
extent which is the greater the more the cover deviates from the standard thick-
ness. This holds true even when the object glass has been adjusted by the
ordinary and well-known means to the special thickness of cover that is being
used.
If, for instance, an objective developes its highest possible capacity of performance
with a cover having a thickness of one two-hundredths of an inch it will then, as
every experienced microscopist knows, suffer a considerable reduction in its

page_text: efficiency when a cover glass of one one-hundredth of an inch is used; and this
is true even when the objective, as constructed after the best methods now in use,
has been adjusted for this latter thickness as perfectly as is possible.
What is true of covering glasses thicker than one two-hundredth of an inch is
also true of those which are thinner, and also with objects which are uncovered.
This deterioration or lessening of efficiency arises from a chromatic over correction
where the covering glasses are too thin, and a corresponding under correction
where they are too thick, and is due to the method of adjustment now in use by
our best makers, and which consists in changing the relative distances of the
lenses composing the system.
In order to obviate the defect just described a glass disc with parallel surfaces is
placed in advance of the front lens, which is mounted in the end of a tube adjust-
able on the main setting of the objective. Between this tube and the objective
a highly refractive liquid, such as glycerine, is introduced, which will fill the space
between the front lens and the disc; or when the latter is adjusted to bring it
closer to, the lens will recede to permit of that movement of the disc.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alfred Vincent Newton in the Great Seal Patent Office on the
8th August 1878.
ALFRED VINCENT NEWTON, of the Office for Patents, 66, Chancery Lane, in the
County of Middlesex, Mechanical Draughtsman. "AN IMPROVEMENT IN OBJECT
GLASSES FOR MICROSCOPES." A communication from abroad by Ernst Gundlach
and John Jacob Bausch, of the City of Rochester, in the State of New York, and
Henry Lomb, of Brooklyn, in the State of New York, United States of America.
The object of this Invention is to provide a more effectual means than those
heretofore employed for the adjustment of the object glasses of microscopes to suit
the varying thicknesses of the glass covers of object slides.
The performance of object glasses for microscopes constructed on the plan hitherto
adopted can be perfect only for covers of one thickness, while for covers of all
other degrees of thickness the performance is deteriorated, and this obtains to an
extent which is the greater the more the cover deviates from the standard thick-
ness. This holds true even when the object glass has been adjusted by the
ordinary and well-known means to the special thickness of cover that is being
used.
If, for instance, an objective developes its highest possible capacity of performance
with a cover having a thickness of one two-hundredths of an inch, it will then, as
every experienced microscopist knows, suffer a considerable reduction in its

page_text: efficiency when a cover glass of one one-hundredth of an inch is used; and this is
true even when the objective, as constructed after the best methods now in use,
has been adjusted for this latter thickness as perfectly as is possible.
What is true of covering glasses thicker than one two-hundredths of an inch is
also true of those which are thinner, and also with objects which are uncovered.
This deterioration or lessening of efficiency arises from a chromatic over correction
where the covering glasses are too thin, and a corresponding under correction
where they are too thick, and is due to the method of adjustment now in use by
our best makers, and which consists in changing the relative distances of the lenses
composing the system.
In order to remove this defect it is now proposed to construct the object glass in
the manner shewn in the accompanying Drawing, which is a central section through
the axis of the glass.
The lenses a, b, and c of the system are permanently set in proper positions
relatively to each other. d is a disc or plate of glass or other transparent material
made with two plane surfaces, and fastened in the setting e', which setting con-
stitutes a cup, and is screwed on to the ring e. The ring e, together with the
setting e' of the disc d connected with it, encloses the setting f of the actual
objective with the lenses a, b, c, composing the system. The objective f is adjust-
able by means of a screw g formed on the upper and outer surface thereof, into
which a female screw on the ring e takes. By turning this ring with its attach-
ment e¹ the glass or disc d can be either advanced to and even brought into contact
with the front lens c of the objective, or be moved away from the same.
When the lens c and the glass or disc d are in actual contact the objective is
adjusted for the greatest thickness of covering glass admissible for that objective,
and the combined thickness of both the glasses c and d corresponds to the thick-
ness which the lens c alone ought to have had, so that it, in combination with the
other lenses of the system, might give the best possible image, provided the glass
disc d had been omitted.
With the application of thinner covering glasses however a corresponding increase
becomes necessary in order to retain the greatest possible degree of efficiency.
This required thickening is effected by placing between the disc d and the front
lens can appropriate fluid of as high a refracting power as possible, for instance,
glycerine.
It will be readily seen that by means of the adjustment effected by the screw g,
and the consequent approach or separation of the disc d from the front lens c of
the objective, this fluid layer, which is contained in the cup e¹, will be made corre-
spondingly thicker or thinner, while the adhesion of the fluid particles to the
respective glass surfaces and their cohesion among themselves prevents a disruption
of the connection.
The corresponding thickening of the front lens in the above-described manner,
by means of a layer of an appropriate fluid placed between the front lens c of the
objective and the disc d, affording a direct compensation for the diminution of the
covering glass thickness it is clear that with correct adjustment the corrections
of the aberrations of the objective, and consequently its performance, remain
unaltered.
Furthermore, as the distances between the separate lenses composing the system
remain the same undisturbed by this plan of adjustment, the magnifying power
also remains undisturbed and unaltered, and the working distance is the same
when the object is uncovered as it is when the thickest covering glass admissible
for the objective is employed.
Having now set forth the nature of the Invention of "An Improvement in
Object Glasses for Microscopes," as communicated to me by my foreign corre-
spondents, and having explained the manner of carrying the same into effect, I
wish it to be understood that under the above in part recited Letters Patent I
claim, the combination of the adjustable transparent plate or disc d with the front

page_text: lens c of the objective, the two being connected by a highly refractive liquid, and
the whole operating in the manner and for the purpose substantially as described.
In witness whereof, I, the said Alfred Vincent Newton, have hereunto set
my hand and seal, the Eighth day of August, in the year of our Lord
One thousand eight hundred and seventy-eight.
A 17 AGATION