IMPROVEMENTS IN STEREOSCOPES
Year: 1856

page_text: LETTERS PATENT to Ebenezer Erskine Scott, of Dundee, for the Inven-
tion of "IMPROVEMENTS IN STEREOSCOPES."
PROVISIONAL SPECIFICATION left by the said Ebenezer Erskine Scott
at the Office of the Commissioners of Patents, with his Petition, on the
3rd November 1856.
I, EBENEZER ERSKINE SCOTT, of Dundee, do hereby declare the nature of
the Invention for "IMPROVEMENTS IN STEREOSCOPES," to be as follows:-
Heretofore in the construction of refracting stereoscopes it has been usual
to employ eye pieces, consisting each of half of a smaller portion of a double
convex or other magnifying lens; but in some cases refracting stereoscopes
have been constructed having eye pieces consisting of two entire lenses;
placed at such a distance apart that the observer looks through the centre of
each of them, and the light from the two pictures enters the eyes in parallel
rays, as if it radiated from a single object at a great distance from the
observer.
Now, my Invention consists in the use of eye pieces composed of two
entire lenses placed so that their centres are at a greater distance apart than

page_text: the eyes of the observer, the said distance being either fixed or capable of
adjustment; the effect being that the light from the pictures passes to the
eyes through a portion of each lens more or less within the centre of the same,
and appears to radiate from an object placed at a distance from the observer,
corresponding with that at which the natural objects represented in the stereo-
scope pictures have themselves been distant when they were taken. By using
entire lenses in this manner tho stereoscopic effect is more easily observed
than in stereoscopes constructed with portions of lenses, while the spherical
and chromatic aberrations are both considerably less than in previous lenticular
arrangements, and the combined image retains more completely than in any
former arrangement all the natural effects of distance which belonged to the
original objects represented.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Ebenezer Erskine Scott in the Great Seal Patent Office on
the 28th April 1857.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EBENEZER
ERSKINE SCOTT, of Dundee, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Third day of November, in the year of our Lord
One thousand eight hundred and fifty-six, in the twentieth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Ebenezer Erskine Scott, Her special licence that I, the said Ebenezer
Erskine Scott, my executors, administrators, and assigns, or such others as
I, the said Ebenezer Erskine Scott, 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 STEREOSCOPES," upon the condition (amongst others)
that I, the said Ebenezer Erskine Scott, 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 In-
vention, 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.

page_text: NOW KNOW YE, that I, the said Ebenezer Erskine Scott, do hereby
declare the nature of the said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say:-
All previous constructions of the stereoscope refer to one or other of the
two constructions about to be mentioned.
First, the stereoscope may be constructed with two separate entire lenses,
placed in the instrument at the same distance apart as the eyes of the observer.
In this way the optical axes of the eyes are parallel, the right eye being
directed in a straight line to the right-hand stereoscopic picture and the left
eye to the left picture, and the rays from these objects being thus also parallel,
the combined picture is seen in the same way as very distant objects are seen,
such as the sun, moon, distant hills, &c.
Second, in the instrument as hitherto commonly constructed the opposite
effect is produced, the rays of light from the two pictures being so refracted
by the lenticular arrangements adopted that they emerge from. the eye pieces,
as if they both radiated from a near object as near as the stereoscopic pictures
themselves, that is, about six or seven inches distant. This effect is produced
by using half or quarter lenses, reversed in their positions, and applied so that
the eyes look through the thin outside edges of the glass brought by the re-
versing to the inside of the double eye piece. Both these modes are objection-
able; the first, because few eyes can accustom themselves to look at a near
object as if it were very distant; and the second, for the reverse reason, because
from the unnecessary extent of refraction the combined pictures are shewn
rather as exaggerated miniatures of the real objects, and thus there is wanting
the full degree of natural effect, which should, of course, be the object of the
stereoscopist to obtain, and the attaining of which in a high degree is the per-
fection of the instrument. Besides, according to the ordinary lenticular
arrangements, the refraction being great the colour is much increased, and
spherical distortion converting straight lines into curved lines becomes also
much more apparent. In my arrangement I take a medium course, which
does away with all the above faults, and has other great advantages. I so
arrange the double eyo piece that the rays from the two pictures come to the
eye as if they radiated from a point of medium distance, such as that at which
we are in the habit of looking at natural objects, the effect being, as I have
already experienced in numerous cases, that the eyes of the observer instantly
form the combined picture without the slightest pain to the eyes, and the
reality of the view is consequently much more strongly impressed on the mind,

page_text: and the pleasing illusion much increased. The simple way in which this is
done is by using entire lenses, and placing their centres a little farther apart
than the distance betwixt the eyes of the observer, so that the rays from each
picture are slightly refracted outwards. By this arrangement the chromatic
fault is reduced to an inappreciable quantity, the spherical distortion very
much reduced, and the lenses being each inade of considerable diameter, say,
2 inches, or upwards, it becomes unnecessary to put the eyes close to the
instrument, and the whole effect becomes exactly similar in all cases in which
the views are correctly taken to that in a well-constructed diorama, the stereo-
scopic effect being of course added thereto.
The accompanying Drawing represents what I have found to be a very
advantageous form of the instrument, having my Invention applied thereto.
Figure 1 is a perspective sketch of the complete instrument. It consists of
a box B, the front part of which has ground glass E, E, inlaid therein, as is
represented in Figure 3. Immediately behind the ground glass a perpendicular
slot C, D, Figure 1, is made in the box, open at the observer's right-hand side,
and stretching accross the instrument, so as to allow the stereoscope slides to be
placed in the field of view. A small piece of flat brass or other material works
to a limited extent sideways in the bottom of this slot by means of the milled
head F, represented in Figures 3 and 4, and enables the observer to centre the
pictures, which in their position in the slot rest on this piece of brass. The
front half of the top of the box opens as a lid G, as is represented in Figures 1
and 3, and the inside of the lid being covered with silver or gold foil serves to
reflect light on the pictures in the slot. This lid is retained in any position by
a clip of brass H fastened to it, and clipping on to the longitudinal diaphragm
I, which stretches along inside of the box, serving to divide it in two,
and prevent the observer from seeing more than one of the two views with
each eye at a time. This clip II is represented in Figures 1, 3, and 4, and
the diaphragm I in Figure 4, in plan. The near end of the box B has an
opening in it K, L, M, N, Figure 2, so as to admit the eye piece represented
in Figures 5 and 6, and which slides out so as to suit different eye-sights, as
represented in Figure 1. From the interior view of the eye piece, Figure 6,
it will be observed that it is furnished with a short double diaphragm 0, 0, so
made that in using the instrument a half of this short diaphragm goes on each
side of the longitudinal diaphragm I, before described, and serves at all adjust-
ments of the eye piece effectually to keep the two halves of the box separate.
The box B is also furnished with a transverse vertical diaphragui, fixed at one-
half its length, and having two square apertures therein, P, P, Figure 2, of

page_text: and no more.
sufficient size to enable the observer to see the entire pictures through them
This diaphragm serves to assist in preventing unnecessary light
reaching the eye of the observer, and detracting from the clearness of view of
the pictures. Finally, in Figures 5 and 6 are represented the sizes and
positions of the two lenses R, used to complete the instrument and to adapt it
to my Invention. The box is mounted on a turned or ornamented stand, and
is capable of adjustment as to height by means of a sliding rod fastened to
the box, and a pinching screw, as represented in Figure 1.
In carrying the Invention into practice I have found that the average
distance betwixt the centres of the human eyes being about 2 inches, the
most advantageous average distance apart of the lenses constituting the eye.
piece of the stereoscope is from 24 inches to 21 inches, and a very con-
venient size for each lens is 24 inches diameter, or when set in their
frames, 2 inches aperture, or larger lenses may be employed and cut down
eccentrically, so that in their cut down state, although placed at the same
distance apart as the eyes of the observer, the original centres are farther
apart. At the distance above mentioned the vision of the stereoscopic objects
is perfectly distinct for the great majority of individuals; but in excep-
tional cases, where the eyes are further apart or closer together than the
average, an adjustment may be applied to the instrument, by which the
distance betwixt the centres of the lenses may in each case be adjusted
so as to make the views most distinct and easy of vision to each observer.
Further, the lenses themselves may either be constructed of one material or
made compound or achromatic, and may be of any of the usual forms, plano-
convex, achromatic combinations with the plain surface next to the eyes of
the observer having been proved by me to be a highly advantageous con-
struction. I have to add that my Invention is applicable to all practicable
sizes of stereoscopic pictures, the distance from the eyes of the observer at
which the pictures are placed in the instrument and the relative focus of tho
lenses being adjusted accordingly.
Having now described the nature of my said Invention, and in what manner
the same is to be performed, I, the said Ebenezer Erskine Scott, do hereby
declare that I do not claim as new or the exclusive use of any parts of the
forms of stereoscopes herein described other than the mode of constructing the
eye piece as described by me; but that I do claim as my Invention the use of
eye pieces composed of two magnifying lenses, either entire or modified, as
already described, placed so that their centres are at a greater distance apart
than the eyes of the observer, the said distance being either fixed or capable

page_text: of adjustment, so as to produce the maximum of pleasant effect in the use of
he instrument.
In witness whereof, I, the said Ebenezer Erskine Scott, have hereto
set my hand and seal, this Twenty-fourth day of April, in the year
One thousand eight hundred and fifty-seven, before these witnesses,
John Sturrock, junior, Writer, Dundoc, and Robert Graham Thoms,
Apprentice to me, the said Ebenezer Erskine Scott.
JOHN STURROCK, jun., Witness.
R. GRAHAM THOMS, Witness.
E. ERSKINE SCOTT. (LS.)