SHORT ACCOUNT OF SOME PRINCIPLES RELATING TO ABERRATIONS.
Year: 1895

page_text: I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent
Agents, 45 Southampton Buildings, in the County of Middlesex, do hereby declare
the nature of this invention to be as follows:-
1. SHORT ACCOUNT OF SOME PRINCIPLES RELATING TO ABERRATIONS.
Chromatic aberration is due to the fact that the different colours of the spectrum
have different foci, and spherical aberration is due to the fact that one and the same
colour forms distinct foci according to the height, measured from the centre, at
which its rays fall upon a lens.
A. convergent lens causes the rays of different colours to converge to foci nearer
and nearer to the lens in passing from red to violet, and the rays of one and the
same colour in passing from the centre toward the circumference.
A divergent lens produces the inverse phenomena, causing the viclet to diverge
more than the red and the rays of one and the same colour which fall upon the
edges of the lens than those which fall in the centre.
It is thus seen that on joining two glasses of different dispersive powers, one
convergent and the other divergent, these two defects may be mitigated. But they
can never be nullified.
For the achromatism of the lenses one arranges that two foci, namely those of
the most intense colours of the spectrum, coincide. The foci of the other colours
do not coincide but lie in proximity with one another.
As regards the spherical aberrations they are simply diminished by this com-
bination, the foci corresponding to the different heights are brought together while
preserving the order which they occupy with a simple lens.
One and the same simple lens has on the other hand two different values of
spherical aberrations (unless their curves be equal) according as the light enters
the lens through one or the other face, so that on inverting the same, one obtains
quite different results. It is thus evident that the orientation of a lens given with
regard to the direction of the entering of the light, is of great importance for optic

page_text: A pencil of rays emanating from a very far distant point, forms a convergent
pencil of rays at the principal focus of the object glass. If one places in the path
of these rays a divergent eye-glass such that its focus coincides with that of the
pencil aforesaid, the rays will leave the instrument parallel to the principal axis
and the point from which they have emanated will appear to the eye lying behind
the eye-glass to be at an infinite distance.
It is the opening of the iris or pupil that on the other hand regulates the opening
of the pencil of rays, looked at.
But as we have already stated, the object glass, owing to the aberrations, has not a
unique focus, neither has the eye glass. In order that the image be clear and
achromatic, it is evidently necessary that all emergent rays shall come forth
parallel to the axis, irrespective of what their colour may be and what may be the
corresponding heights, at which they meet the object-glass and eye-glass.
This condition will only be realized when the focus is that of the object glass for
a determined colour and for a certain height, and when at the same time the focus
of the eye-glass or eye-piece for the same colour and for the corresponding height,
coincides with said focus, and when it is the same with all colours and all
corresponding heights.
To sum up, it is necessary that all foci of the object glass and all foci of the
eye-glass for the same colours and corresponding heights, shall coincide, or, in
practice shall be very close to one another.
It is essential to remark that the focus of the object glass is that of the object-
glass for such light which arrives at its front surface and that the focus of the
eye-glass is that of the eye-glass for such rays which arrive at the rear surface.
It is evident that when both lenses are simple, this result can not be attained
with values of slight difference with regard to their focal lengths. In fact, the
shorter the focus of a lens will be, the smaller will be, in absolute value, its
aberrations. If thus the focal lengths are very different, the aberrations will be
likewise so, in absolute value, and the proposed result would not be attained.
It is seen on the other hand that when the object glass is composed of two joined
lenses, and its aberrations are diminished, a simple eye-glass of short focus may be
united therewith, the aberrations of which will be substantially equal and the
images of the system will be clear.
In practice one obtains object-glasses with such aberrations that one can not give
to the eye-glass a focal length which is appreciably less than one fifth of that of
the object glass. And in commerce one only finds field or marine glasses, the
magnifying power of which does not exceed 5; and all attempts to make such
glasses with a higher magnifying power than 5 results in instruments that give
indistinct and blurred images.

page_text: vague. This defect is frequently met with but is on the other hand, at least in
certain instruments only slightly noticeable. On placing or adjusting for instance
the central parts of the object to be viewed, well in its viewing point, the edges of
the image appear slightly fogged or, to use the term of opticians, the image loses
at its edges.
(c.) DEFORMATIONS OF THE IMAGES.
A third defect often met with in double glasses is the inward curving of the
straight lines of the object caused by the spherical aberrations and the proportional
heights of the image. But this fault is corrected simultaneously with the preceding
one by the exact superposition, from point to point, of the curves of aberration.
In short it results from the preceding observations that the Galileo telescope
can in fact not be free from those three defects mentioned, unless the aberrations of
the object-glass and those of the eye-glass exactly compensate one another.
It does not lie within the scope of this Specification to develop the calculations
which lead to the desired result. As already stated, it results from these
calculations that the assemblage of two glasses for forming the object glass does
permit of compensating in a satisfactory manner only those aberrations of a simple
eye-glass which has its focus about five times smaller.
When the eye-glass itself is composed of two assembled glasses, its aberrations
are diminished and even this proportion can not be attained. It has likewise not
yet been possible to produce suitable opera glasses having their eye-glass composed
of several glasses except by using object-glasses of short foci and by composing the
object glass as well as the eye glass no longer of two but of three assembled glasses
so as to greatly diminish the aberrations of each of them, to such an extent as to
render them practically indifferent.
These are the glasses, known in commerce under the name "field or marine
glasses with 12 leuses."
But if the magnifying power of said glasses is to be further increased to a point
hitherto impossible to attain it is necessary to work toward this double purpose
viz. to diminish the aberrations of the object glass and to increase those of the eye
glass and to achieve this purpose not to experiment with compound eye glasses but
with simple eye-glasses.
Finally one grave inconvenience which would be inherent to powerful glasses
could they be clear, is the small field of view which they would then possess.
In fact the angle under which the magnified image of the object or the amplified
rea is viewed, is nearly equal to the angle under which one sees the opening of
he object glass from the optic centre of the eye glass. For a given opening of
he object glass it is found that the more the distance from the eye glass to the

page_text: object glass increases, the smaller will this angle become, and as on the other hand
the magnifying power increases simultaneously with this distance; thus for a two
fold reason the real field of view, as quotient of the area into the magnifying
power, is more and more diminished.
It must on the other hand also be observed that, for field or marine glasses or
optic instruments with a double body, the maximum opening of the object glass
is limited to about 60 milimeters, being the medium distance of the focal distance
of the eyes.
III. ARRANGEMENTS OF THE FIELD OR MARINE GLASS FORMING THE
OBJECT OF THIS INVENTION.
The object glass or objective is composed of two ordinary double object glasses
placed at a certain distance apart from one another. Calculation shows that by
this arrangement the aberrations are smaller than those of a single object glass of
the same focus. The same is the case when the second object glass is of one simple
glass. In all cases the aberrations are smaller when the convex part of the object
glasses are turned toward the side where the light enters.
The first object-glass alone would produce from a far distant object a real,
reversed image; the interposition of the second object-glass, substitutes for this
image another image, which is likewise a real and reversed one.
Finally a simple eye glass placed to receive the pencil of rays, which would
form the second image produces, as in the Galileo telescope, a right and virtual
image.
For increasing the aberration of this simple eye-glass for such rays which arrive
in the contrary sense of the direction of the light, it is necessary that the most
prominent part of the concavity be turned toward the eye. This eye-glass bas
on the other hand a very short focal length and the employment of which had
up to the present time never been risked owing to reasons which I have herein-
before given.
As by this double arrangement the aberrations of the object glass have become
very small, whilst those of the eye-glass, in the suitable direction, have been made
as large as possible, one can arrive as far as to give them equal values and, as we
have seen, one can avoid the different defects above mentioned.
Also in the practical application I have been able to employ simple eye-glasses
with very short focal lengths (10 millimeters) whereas the simple glasses used up
to the present time have a focal length not less than 35 millimeters. By this
means I construct field or marine glasses which magnify 10 and 12 times.
Finally by this arrangement the field of view is considerably amplified.
In fact, as the ray which passes through the centre of the eye-glass and through
the edges of the object-glass is no longer a straight line but a broken line, namely
broken by the object glass the latter causing the same to converge, the amplified
field of view is equal to the angle an angle which is evidently larger than the angle
before subtended. As now the length of the instrument is less with this
combination than with the simple eye glass, this latter augle is itself larger than
the amplified field of view which one would have obtained therewith. Thus, the
amplified field of view of our combination is larger than that which would have
been obtained by the ordinary Galileo glass of the same magnifying power.
To recall to mind this advantage, we give to the second object glase the name
field glass. In practice we have proceeded to double the field of view of the field
or marine glasses constructed according to previous processes.
A last advantage of this system consists in the diminution of length of the
instrument for a given value of magnifying power; it results on the other hand
immediately from the use of eye-glasses of much shorter focus.
The achromatism can be obtained in the following manner:
(1.) By employing a simple field lens of crown glass and likewise a simple

page_text: eye-glass of crown glass or Hint glass. The use of flint glass is preferably because
it allows of placing the field lens still further from the eye-glass and to obtain a
greater increase of field of view and a greater reduction in length of the instrument.
The simple field lens does not allow of reducing the focal length of the eye-glass
below 20 to 18 millimeters.
(2.) By employing as field lens an achromatic object glass for central rays and a
simple eye glass of crown glass. The small defect of achromatism for the
marginal rays of the object glass and of the field lens is then compensated by
the chromatic aberrations of contrary direction of the eye glass. With this field
lens one can reduce the focal length of the eye glass down to 10 to 12 millimeters.
In 1834 Monsieur Charles Chevalier obtained a French Patent issued
September 6th on opera glasses with two object glasses, of which the eye glass was
double.
In 1850 he took out a second French Patent No. 10697 October 30th for the
same arrangement; the eye glass only being modified and composed of three
assembled glasses. It is thus principally this modification which he intended to
have protected by Patent; the first Patent of addition taken on the 28th of
August 1851 is entirely devoted to the different forms which may be given to this
eye glass of an entirely particular combination.
As will be understood from the theoretical developments which have been
successively explained in the beginning of this Specification, it was impossible with
this system of eye glass with very small aberration, to arrive at higher magnifying
powers than those obtained till then. Also, in fact, Charles Chevalier has never
constructed a model of his megascopic glasses except in the customary values of
magnifying power. The clearness of the images was likewise rather considerably
diminished precisely by an inequality between the respective and corresponding
aberrations of the eye glass and of the arrangement of the two object glasses. The
field of view was slightly amplified but this amplification was of such little
importance that the inventor had at first not observed it and he did not mention it
in his Patent. It was only later on that he speaks in his catalogue of this
peculiarity of the megascopic opera glasses.
It results from all the preceding observations that the differences which this
improved system presents above that of Monsieur Charles Chevalier (and the
principal ones of which are:
A constant use of the simple eye glass with unequal curves, the strongest
being placed toward the eye.
The use, as the case may be, of a simple or compound field lens,)
are sufficient to ensure entirely different and greatly superior results as compared
with those he had obtained with his megascopic opera glasses.
If one will simply take the advantage of the increase of field of view by merely
realizing magnifying powers which have already been obtained, it cau not be
necessary to so much increase the aberrations of the eye glass and to impart to the
latter equal or nearly equal curves.
C 1008

page_text: Chromatic aberration is due to the fact that the different colours of the spectrum
have different foci, and spherical aberration is due to the fact that one and the same
colour forms distinct foci according to the height, measured from the centre, at
which its rays fall upon a lens.
A convergent lens as shown in Figure 1 causes the rays of different colours to
converge to foci nearer and nearer to the lens in passing from red to violet, and
the rays of one and the same colour to pass from the centre toward the circum-
ference as seen in Figure 2.
A divergent lens produces the inverse phenomena, causing the violet to diverge
more than the red Figure 3 and the rays of one and the same colour which fall
upon the edges of the lens than those which fall in the centre Figure 4.
In Figures 1 and 3, R" designates the white rays, f the violet focus, and the
yellow focus, and fr the red focus.
In Figures 2 and 4, respectively designate the foci corresponding to
the rays at heights h, h', h
It will thus be seen that on joining two glasses of different dispersive powers,
one convergent and the other divergent, these two defects may be mitigated, but
they can never be nullified.
For the achromatism of the lenses two foci namely those of the most intense
colours of the spectrum, are so arranged that they coincide. The foci of the
other colours do not coincide but lie in proximity with one another.
As regards the spherical aberrations, they are simply diminished by this com-
bination, the foci corresponding to the different heights
are brought
together while preserving the order which they occupy with a simple lens.
One and the same siniple lens has on the other hand two different values of
spherical aberrations (unless their curves be equal) according as the light enters
the lens through one or the other face, so that on inverting the same, one obtains
quite different results. It is thus evident that the orientation of a lens given with
regard to the direction of the entering of the light, is of great importance for
optical instruments.

page_text: This combination constitutes the field or marine glass with 6 lenses. I will
hereinafter add some remarks with regard to the field or marine glass with
12 lenses.
(a.) CLEARNESS OF THE PICTURES.
The rays A B emanating from a very distant point, forms a convergent cone of
rays at F, the principal focus of the object glass O. If a divergent eye-glass ()
is placed in the part of these rays so that its focus f coincides with F, the rays will
leave the instrument parallel to the principal axis and the point from which they
have emanated will appear at an infinite distance to the eye at X behind the
eye-glass Figure 5.
It is the opening I of the iris or pupil that on the other hand regulates the
opening of the cone of rays, looked at.
But as we have already stated, the object glass, owing to the aberrations, has
uot a unique focus, neither has the eye glass. In order that the image be clear
and achromatic it is evidently necessary that all emergent rays shall be parallel to
the axis, irrespective of their colour and the corresponding heights h and h, at
which they meet the object-glass and eye-glass Figure 6.
This condition will caly be realised when the focus is that of the object glass
for a determined colour and for a certain height 1, and when at the same time the
focus of the eye-glass or eye-piece for the same colour and for the corresponding
height, coincides with said focus F, and when it is the same with all colours
and all corresponding heights.
To sum up, it is necessary that all foci of the object glass and all foci of the
eye-glass for the same colours and corresponding heights, shall coincide, or, in
practice shall be very close to one another.
It is necessary to state that the focus F is that of the object-glass for such rays
received at its front surface and that the focus is that of the eye-glass for rays
received at the rear surface Figure 6.
It is evident that when both lenses O and O' are simple, this result can not be
attained with values of slight difference with regard to their focal lengths. In
fact, the shorter the focus of a lens, the smaller will be, in absolute value, its
aberrations. If thus the focal lengths of O and O' are very different, the
aberrations will be likewise so, in absolute value, and the proposed result would
not be attained.
It will be seen on the other hand that when the object glass is composed of two
connected lenses, and its aberrations are diminished, a simple eye-glass of short
focus may be united therewith, the aberrations of which will be substantially equal
and the image or definition given will be clear.
In practice object-glasses are obtained with such aberrations that one can not
give to the eye-glass a focal length which is appreciably less than one fifth of that
of the object glass. And in commerce one only finds field or marine glasses, the
magnifying power of which does not exceed 5; and all attempts to make such glasses
with a higher magnifying power than 5 result in instruments that give indistinct
and blurred definition.

page_text: which is toward the object glass; the focus F° for central rays being longer than
the focus Fh of the cone of rays, the axial ray falls at a distance from the
centre Figure 8.
On the other hand, in order that a real image, the different cones of rays of
which meet the eye-glass, may give, by the interposition of said eye glass, a virtual
level image (of which for instance all points meet at infinity see Figure 9) it is
necessary that each point P1 of each image be in the focal plane P which
corresponds to the height ', at which the axis of the cone of rays meets the eye
glass. The spherical aberration causes, as we have seen, this focus to vary with
the height ', and is so much shorter as the height is greater; it follows that
the image must have a curve in the same sense as that illustrated in Figure 8.
When these two curves become superposed that is to say when that of the real
image of the object-glass has precisely the form, caused by the aberrations of the
eye-glass, the telescope gives clear images in all points of the field of view.
When these curves differ, certain parts of the image which are in proximity to
the points of intersection of the two curves are clear and the others indistinct and
vague. This defect is frequently met with but is on the other hand, at least in
certain instruments only slightly noticeable. On placing or adjusting for instance
the central parts of the object to be viewed, well in its viewing point, the edges
of the image appear slightly fogged, or to use the term of opticians, the image
loses at its edges.
(c.) DEFORMATION OF THE IMAGES.
A third defect often met with in double glasses is the inward curving of the
straight lines of the object. This incurvation is due to the fact that owing to the
spherical aberrations, proportional heights of the object do not give rise to
proportional heights of the image. But this fault is corrected simultaneously
with the preceding one by the exact superposition, from point to point, of the
curves of aberration.
In short it follows from the preceding observations that the Galileo telescope can
not in fact be free from the three defects above mentioned, unless the aberrations
of the object-glass and those of the eye-glass exactly compensate one another.
It does not lie within the scope of this Specification to demonstrate the calcula-
follows from these
tions which lead to the desired result. As already stated,
calculations that the arrangement of two glasses for forming the objective permits
of compensating in a satisfactory manner only those aberrations of a simple
cye-glass which has its focus about five times smaller than that of the objective.
When the eye-glass itself is composed of two assembled glasses, its aberrations
are diminished and even this proportion can not be attained. It has likewise not
yet been possible to produce suitable field or marine glasses having their eye-picces
composed of several glasses except by using object-glasses of short foci and by
forming the object glass as well as the eye glass not of two, but of three assembled
glasses so as to greatly diminish the aberrations of each of them, to such an extent
as to render them practically indifferent.
These are the glasses, known in commerce under the name
glasses with 12 leuses."
"field or marine
But if the magnifying power of said glasses is to be further increased to a
point hitherto impossible to attain, it is necessary to work toward this double
purpose viz. to diminish the aberrations of the object glass and to increase those
of the eye glass and to achieve this purpose not to experiment with compound eye
glasses but with simple eye-glasses.

page_text: or the amplified area is viewed, is nearly equal to the angle under which one sees
the opening of the object glass from the optic centre of the eye glass. For a
given opening of the object glass it is found that the greater the distance from the
eye glass to the object glass, the smaller will this angle become, and as on the other
hand the magnifying power increases simultaneously with this distance; thus for a
twofold reason the real field of view, as quotient of the area into the magnifying
power, is more and more diminished.
It must on the other hand also be observed that, for field or marine glasses or
optic instruments with a double body, the maximum opening of the object glass is
limited to about 60 millimetres, being the medium distance of the focal distance of
The you
ARRANGEMENT OF THE FIELD OR MARINE GLASSES FORMING THE OBJECT
OF THIS INVENTION.
The objective is composed of two ordinary double object glasses 01, 02, placed
at a certain distance apart. Calculation shows that by this arrangement the
aberrations are smaller than those of a single object glass of the same focus. The
same is the case when the second object glass O2 is of one simple glass. In all
cases the aberrations are smaller when the convex part of the object glasses O'
and O2 are turned toward the side where the light enters see Figure 11.
The first object-glass O' alone would produce from a far distant object A Ba
real, reversed image A' B'; the interposition of the second object glass 0³,
substitutes for this image another image A2 B2, which is likewise a real and
reversed one.
Finally a simple eye glass O' placed to receive the cone of rays, which would
form the second image A2 B2 produces, as in the Galileo telescope a right and
virtual image A¹ B'.
For increasing the aberration of this simple eye-glass for such rays which arrive
in the contrary direction to that of the light, it is necessary that the most
prominent part of the concavity be turned toward the eye. This eye-glass has ou
the other hand a very short focal length and the employment of which has up to
the present time never been risked owing to reasons which I have hereinbefore
given.
As by this double arrangement the aberrations of the object glass have become
very small, whilst those of the eye-glass, in the suitable direction, have been made
as large as possible, one can go so far as to give them equal values and, as we have
seen, the different defects above mentioned can be avoided.
Moreover in the practical application I have been able to employ simple eye
glasses with very short focal lengths (10 millimetres) whereas the simple glasses
used up to the present time have a focal length of not less than 35 millimetres.
By this means I construct field or marine glasses which magnify 10 and 12 times.
Finally by this arrangement the field of view is considerably amplified.
In fact, as the ray which passes through the centre of the eye-glass and through
the edges of the object-glass is no longer a straight line but a broken line A. A'0',
uamely broken by the object glass the latter causing the same to converge, the
amplified field of view is equal to an angle A' O'B' which is evidently larger than
the angle A. O' B. As now the length O'O' of the instrument is less with this
combination than with the simple eye glass, this latter angle A O' B is itself
larger than the amplified field of view which one would have obtained therewith.
Thus, the amplified scope of view A¹ O B¹ of our combination is larger than that
which would have been obtained by the ordinary Galileo glass of the same
magnifying power.
To recall to mind this advantage, we give to the second object glass O² the name
field lens. In practice we have proceeded to double the field of view of the field
and marine glasses constructed according to previous processes.

page_text: A further advantage of our system consists in the diminution of length of the
instrument for a given value of magnifying power; it results on the other hand
immediately from the use of eye-glasses of much shorter focus.
The achromatism can be obtained in the following manner:
1. By employing a simple field lens O' of crown glass and a simple eye-glass of
crown glass or flint glass. The use of flint glass is preferable because it allows of
placing the field lens still further from the eye-glass and to obtain a greater
increase of field of view and a greater reduction in length of the instrument. The
simple field lens does not allow of reducing the focal length of the eye-glass
below 18 to 20 millimeters.
2. By employing as field lens an achromatic object glass for central rays and a
simple eye piece of crown-glass. The small defect of achromatism for the marginal
rays of the object glass and of the field lens is then compensated by the chromatic
aberrations of contrary direction of the eye glass. With this field glass one can
reduce the focal length of the eye glass down to from 1 to 12 millimeters.
In the year 1814, Mr. William Francis Hamilton patented an optic apparatus
No. 3781. This Specification does not illustrate or show the use for which the
instrument is designed nor does it explain in what the improvement consists that
results from the combination described. It is however probable that the apparatus
is a telescope destined to obtain an amplified view of distant objects; at any rate
this instrument differs from that herein before described in the following respects
(1) The substantial combination of Hamilton's system comprises one element or
constituent part in addition to the present combination. The former comprises in
fact 2 achromatic object glasses, one simple converging lens and one simple
concave eye glass; the latter comprises one object glass, one converging field lens
(object or simple glass) and one simple concave eye glass.
2. The convex lens and the concave lens arranged close to one another, form oue
whole having as their principal object, as stated by Mr. Hamilton to constitute a
compound achromatic and aplanatic eye glass. The substances and the curvatures
are combined so as to produce this result; this eye glass would thus be nothing
else than an ordinary concave achromatic eye piece, the constituent glasses of
which instead of being applied closely against one another, are only a small
distance apart.
In short, the object Mr. Hamilton has in view is evidently to obtain separately,
in the object glass device on the one hand and the eye glass device on the other
hand, the achromatism and the aplanatism.
In the combination forming the subject matter of the present invention
achromatism as well as aplanatism only exist in the final image namely that which
the eye views or observes; it is therefore the whole of the constituent parts of the
system which is so combined as to be achromatic and aplanatic, each of which
taken apart being not so, and being so combined that when placed a suitable
distance apart from the others, the algebraical sum of the spheric and chromatic
aberrations is nil in the ultimate analysis. It is precisely this method of combining
the constituent parts which allows of withdrawing the field lens a greater
distance from the eye glass and of thus obtaining a considerable increase of field
of view.
PATENTS OF MR. CHARLES CHEVALIER.
In 1834 Monsieur Charles Chevalier obtained a French Patent issued
September 6th on opera glasses with two object lenses, of which the eye glass
was double.
In 1850 he took out a second French Patent No. 10697 October 30th for the
same arrangement; the eye glass only being modified and composed of three
assembled glasses. It is thus principally this modification which he intended to
have protected by Patent; the first Patent of addition to the above Patent taken
on the 28th of August 1851 is entirely devoted to the different forms which may be
given to this eye glass of particular combination.

page_text: As will be understood from the theoretical developments which have been
successively explained in the beginning of this Specification, it was impossible with
this system of eye glass with very small aberration, to arrive at higher magnifying
powers than those obtained till then. Also, in fact, Charles Chevalier has never
constructed a model of bis megascopic opera glasses except in the customary
values of magnifying power. The clearness of the images was likewise rather
considerably diminished precisely by an inequality between the respective and
corresponding aberrations of the eye glass and of the arrangement of the two
object glasses. The field of view was slightly amplified but this amplification was
of such little importance that the inventor did not at first observe it and he did not
mention it in his Patent. It was only later on that he speaks in his catalogue of
this peculiarity of the megascopic field or marine glasses.
It follows from the preceding observations that the differences which this
improved system presents above that of Monsieur Charles Chevalier and the
principal ones of which are a constant use of the simple eye glass with unequal
curves, the strongest being placed toward the eye. The use, as the case may be,
of a simple or compound field lens are sufficient to ensure entirely different and
greatly superior results as compared with those he had obtained with his
megascopic field or marine glasses.
If one will simply take the advantage of the increase of field of view by merely
realizing magnifying powers which have already been obtained, it can not be
necessary to so much increase the aberrations of the eye glass and to impart to the
latter equal or nearly equal curves.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, as communicated to
me by my foreign correspondents, I declare that what I claim is :-
A field or marine glass substantially comprising a combination of three con-
stituent bodies (see Figures 11, 12 and 13) that is to say (1) A compound object
glass, the convex surface of which is turned toward the light; (2) A field lens
(either simple or compound, as the case may be), the convex surface of which is
turned in the same direction as the convex surface of the object glass; (3) A
simple eye glass (bi-concave, plano-concave or meniscus shaped) the concave
surface of which is turned toward the eye of the observer, the three constituent
bodies hereinbefore indicated being so combined as to annihilate the spheric and
chromatic aberrations in the images resulting from the said combination without
each one of the said constituent bodies taken separately, or any two of them, taken
together, constituting of necessity an achromatic or aplanatic body or system.
Dated this 11th day of September 1895.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.