CERTAIN CONSIDERABLE IMPROVEMENTS IN THE CONSTRUCTION OF TELESCOPES, MICROSCOPES, SPECTACLES, AND ALL OTHER INSTRUMENTS OF VISION, EITHER BY REFLECTION ALONE OR COMPOUNDED OF REFRACTION AND REFLECTION, WHEREBY THE FIELD OF VIEW IS GREATLY EXTENDED, AND THE OBJECTS RENDERED MUCH MORE DISTINCT THAN AT PRESENT
Year: 1785

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HUGH
DIXON, of the Parish of Saint James, Clerkenwell, and County of Middlesex,
Chymist, send greeting.
WHEREAS His most Excellent Majesty King George the Third did, by
His Letters Patent under the Great Seal of Great Britain, bearing date the
Fourteenth day of December, in the twenty-sixth year of His reign, give and
grant unto me, the said Hugh Dixon, His especial licence that I, the said
Hugh Dixon, during the term of years therein expressed, should and law-
fully might use, exercise, and vend, within England, Wales, and the Town of
Berwick-upon-Tweed, my Invention of "CERTAIN CONSIDERABLE IMPROVEMENTS
IN THE CONSTRUCTION OF TELESCOPES, MICROSCOPES, SPECTACLES, AND ALL OTHER
INSTRUMENTS OF VISION, EITHER BY REFLECTION ALONE OR COMPOUNDED OF
REFRACTION AND REFLECTION, WHEREBY THE FIELD OF VIEW IS GREATLY
EXTENDED, AND THE OBJECTS RENDERED MUCH MORE DISTINCT THAN AT PRESENT;"
in which said Letters Patent there is contained a proviso obliging me, the
said Hugh Dixon, under my hand and seal, and to cause a particular descrip-
tion of the nature of my said Invention, and how the same is to performed,
to be inrolled in His Majesty's High Court of Chancery within one calendar
month next and immediately after the date of the said recited Letters Patent,
as in and by the same (relation being thereunto had) may more fully and
at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Hugh Dixon, do hereby declare that my said Invention is described in
manner following (that is to say):
The possibility of improving optical instruments, and so as to view objects
by reflexion only, or reflection and refraction jointly or seperate, is supposed
generally allowed, and an instance of proportion of any improvement may be
more useful than a minute description of every possible proportion or vari-
ation; the principle being made known, the different proportions made be
made use of at pleasure.
.
Telescopes. The telescope commonly called Gregorian, as to combina-
tion. Suppose the great metal speculum or concave mirror (on which the
rays of light first impenge) to be 6 inches in diameter, the focus (called
principal) to be 31 inches, or say, radius 63 inches; the small speculum,
if a concave mirror, to be about one inch and three quarters diameter, and
principal focus to be 61 or 5 inches, as the shortest focus for admitting
the whole picture or image of the sun through the hole or apperture in
the center of great concave speculum, which hole or apperture to be not
less than one inch and 7/5ths of an inch diameter; such a proportion will
admit the picture of the sun to pass through the hole in great speculum as
first formed in its principal focus, and reflected by the small speculum, and to
again form upright and at any reasonable distance beyond the great speculum,
and until that picture or image of the sun be formed as large as the diametor
of the great speculum, or larger. The picture of the sun formed in the
principal focus of a concave mirror is near about one tenth part of an inch
for cach foot of focus; therefore, say, in the present instance, the first picture
or image to be about two tenths and 5 eighths of a tenth; then, if the radius
of the small speculum is 10 inches and inch (or 5 inches principal focus),
the second picture, if formed at about 15 or 16 inches from the back of great
speculum, will be about two inches and of an inch in diameter; and if the
distance from back of great speculum is about 18 or 19 inches, say, picture
about 3 inches in diameter, and at 38 inches the picture about 4 inches
diameter, the screw that regulate the distance of small speculum to contain
25 threads or rounds in an inch length. To form the first picture of two
inches and diameter, the adjusting screw may be turned about seven rounds
to bring the small speculum nearer the great speculum than for the usual eye
glasses station; and if the second mentioned diameter of picture of about
3 inches, say turns of screw nearer to great speculum, about or full eight
turns, but the four inch picture requires near about 12 turns. The focus and
diameter of the eye glasses are arbitrary, as the telescope. maker may be

page_text: pleased to adjust, or as the perfection of the instrument will bear, or the mag-
nifying powers are either given by the focus of the small speculum, or by the
focus of the eye glasses, in the usual form or combination. But in this
improvement the tube or piece containing the eye glasses being removed, and
a convex metal speculum of near one inch and seven eighths of an inch
diameter, and of a vegative or virtual focus of 31 inches and inch being
placed near or in, before or behind the hole in center of great speculum, and
at an angle of about 10 or 12 degrees, but so as to reflect the light that is to
form the picture of the object, say, at about eight inches from the object erd
of the telescope; and the center part of that picture to be about six inches
clear off from a line supposed to pass through the centers of small and great
speculums. The tube is supposed, in this case, formed on purpose, or the side.
of the old tube removed and altered, and at the distance of about one or
3 inches from the object end; a concave mirror of five or more inches
diameter, and 8 or 10, or say 7 inches or less, principal focus, and at an angle
of 6 or 8 or more degrees in respect of the center of the great speculum, in
order that the viewer's head may be clear from obstructing the rays that are
proceeding to form the picture in or near the focus of that speculum. Such
a construction, when the small speculum is adjusted, will do to view land
objects, or the planets and their satellites, without any glass. An eye station
gage place is proper for viewing the planets, and an apperture hole for land
objects. The eye speculum may be changed for one of less focal length, if
extream degrees of magnifying power is desirable; otherways the convex spe-
culum at center of great speculum may be changed for one of 25 or 20
or less number of inches principal virtual focus. But if a less degree of
magnifying power is desirable, than a plane mirror may be used. And,
farther, it may be effected by bringing the eye speculum nearer the middle
part of the tube, as to distance between each extream end, if the speculums
are again adjusted; again, if the length of the telescope is desired as short
as well may be, and no objection to an inverted picture, then a convex small
speculum may be used instead of, and of a negative or virtual focus in respect
of that before used at the object end as the second speculum in use, and then
there will be but one picture formed, and that at or rather short of the
principal focus of the eye station concave speculum.
Further, it belongs to the plan to assert that wether the second or small
speculum, if either concave or convex, should be made choice of, as either a
little larger or less focus length; yet a telescope, by being allowed to be
longer or shorter with the same great speculum, may be made to magnify, a
like length of tubes or telescope being allowed for longer focus small speculum..

page_text: Variation to the above-mentioned great and small speculum:-Place a
concave speculum near center of great speculum (instead of the convex), and
let this concave be of same radius as the great speculum, but diameter suitablé
to the apperture hole in center of great speculum, that wether placed in center
or within or without side, it may be adjusted at its proper angle for reflecting
the picture to the focus, or near the focus of eye speculum, which eye
speculum may be of shorter focus and less diameter than in the first-mentioned
instance, and yet the field of view very large, for the great speculum itself may
be used a second time instead of the third speculum, in or near its center, but:
then the telescope would be pointed a little on one side the object.
Variation farther :-The great and small speculum, say two first as before,.
and the rays of light suffered to proceed through the apperture hole of great
speculum to form a picture or image of the sun at about 18 inches from the
back part of the great speculum. A concave metal speculum, placed. at
26. inches distance from back of great speculum, at an angle of a few degrees
to allow room for part of the head of the viewer, and that speculum of diameter,
say, about four inches, would be more than sufficient to receive the whole-
diameter of the sun's picture; and, if only sixteen inches radius, would.
magnify near about 60 times, and vision distinct with only three speculums.
But the picture would be inverted, in respect of sides right to left, though
upright; and if the second or small speculum was a convex instead of a
concave form, then there would be but one picture formed, and that near the
focus of the third, or eye speculum, and inverted top to bottom part, and right
sto left hand, and viewed with the back toward the real object, and the viewer
looking downward with the same angle that the real object has elevation; but
a fourth speculum, placed near the back of great speculum, or within the focal
distance of the third speculum, according to the figure or form of the three
last speculums, would much alter the position of the object's picture and
apparent place, for, if the fourth speculum is plane, and placed within the
focal distance of third speculum, and at an angle short of 45 degrees for the
viewer, the object will be seen in a direction crossing the axis of the tube;
and if the second or small speculum was convex, the picture will now be
set right as to sides; and if the second speculum was concave, then the second
picture is seen in proper position. This fourth or plane speculum needs only
a small diameter and oval form; but if the third speculum is either a plain
form or convex, then the fourth must be a concave; and say, if six inches
diameter and sixteen inches radius, and its back placed towards the back of
great speculum, and at an angle of few degrees for the beholder's eye station,
near the principal focus, the object will be seen in proper position, and a little

page_text: on one side the direction of bearing of the telescope. If the third speculum is a
plane mirror, and placed at a sinall angle for throwing or reflecting back the
light to the fourth speculum, to form the image near its principal focus, the
angle must be lessened as the plane mirror's distance is increased; if the fourth
speculum retains its station, and according to the distance of the third and
plane mirror if greater, so will the magnifying power be greater; but the
second speculum is to be screwed nearer great speculum, according to the
encrease of distance of the third or plain mirror. In all the above-mentioned
instances the picture of the object is viewed by reflected light, but a concave
glass of 31 inches, or less negitive focus, may be placed near the back of
great speculum, which would shorten the necessary distance of the third
concave speculum where three reflections are used or four, and that glass
would encrease the magnifying power. But I have preferred the effect all by
reflection; and if the second and third speculums are convex, very great degrees
of magnifying power is acquired with shortness of the instrument; and the
hole in great speculum to be smallest, but a thin piece of metal plate or collar
should be fixed at back of the small speculum, as large at hole apperture
in great speculum, to prevent extraneous light. The four metal speculums
may be all concave form, the first and third of same focus and diameter, and
the second and fourth alike, the third being placed at any reasonable distance
behind the first, so that the picture of the sun do not exceed six inches
diameter, and at a small angle to reflect the light which has formed the second
picture, and to be viewed by the fourth speculum, placed with its back part
toward the great speculum, and at a small angle, for the viewer to receive
them without obstructing the light, and the station to be a little within
the distance of their converging to a point as the greatest distance possible,
but a less distance would magnify more.
Reflection and refraction jointly.-The great and small speculum, as in first
instance, and a plane mirror at or near center of great speculum, and at an
angle of about 12 or 10 degrees or less, according to what distance the
light is reflected towards the other end or middle part of the side of the
tube, where, if near the middle part, another plane mirror of oval extension,
shortest diameter about 3 inches, and placed at an angle of about 33 degrees,
or so as to receive and reflect the rays from the other plane at a right angle
across the tube, where, with one or two eyeglasses of larger diameter and
focus than usual, or the usual eyeglasses, the object or its second picture
may be viewed and magnified about twice as much as the old way.
But if this last-mentioned plane mirror is placed nearer the object end, accom-
panied with the eyeglasses and the plane mirrors adjusted, as also the small
speculum, the magnifying power is yet greater, and the eyeglasses as well as

page_text: the plane mirror may be fixed in the axis part of the tube for elevation, the
parts being made on purpose, and the tube part moveable, so that the axis
parts may be either near the middle or the object end; and in this improve-
ment the viewer may keep his same station and posture for any elevation,
always looking horizontally, but changing his station only for objects that have 5
horizontal difference. Objects are seen erect, but if the second or small speculum
is convex the object will appear inverted; the third speculum would bear to be
a small degree convex without much hurt to the form of the image.
Variation. The first and second speculums as in first instance, and the
plane speculum in or near center of the great one, and placed at an angle
of a few degrees to reflect the light of the first picture to the side of the object
end of the tube, where, being placed, the large plane mirror which again
reflects back the light of the first picture to near the edge of great speculum,
where, the eyeglasses being affixed and the small speculum adjusted, the
object is seen very much magnified and erect, and the viewer in position as
with the old construction, the third and fourth, or the plain speculums, one or
both, may be exchanged for the convex form of 63 inches or less or greater
radius, or one of them for a concave of long radius; but the cyeglasses then
ought to have greater diameter and longer focus than usual. This method
takes a good advantage for smallness of degree of angles between the third
and fourth speculums; the eye apperture hole will need adjusting for some of
the variations.
Another method which lengthens the telescope, but is very simple by an
addition of tube to the eye piece of the old form, say great speculum, as
in first instance, 63 inches radius, and small speculum ten and a half
inch radius, a tube of 18 inches length, added to the usual length of the eye-
piece tube, and the glass nearest the object end six inches focus, and the
glass nearest the eye of two inches and one half inch focus, distance about
four inches from each other; screw the small speculum about seven turns
nearer the great speculum, and the magnifying power will be found about 120,
while the old construction was about 60.
Variation. To shorten the length and enable the viewer to manage the
screws for elevation and horizontal direction without using a long hand turner
for the screws, a plain mirror may be used at near the end of additional tube,
which tube may be wider towards the great speculum, and admit of fixing the
eyeglasses at a small angle, so as to view the picture of the object with the
back toward the real object, or else a plane speculum near center of great
speculum, and at an angle to reflect the light from first picture to form the
second near the middle of the telescope, or near the object end yet near the
side, allowing room for the viewer's head, for the plane speculum may be

page_text: set at any sufficient angle for that purpose without injury to the picture; but
the image will be inverted as to sides right and left, and the viewer looks
downward for objects which are elevated.
Newtonian construction of telescopes improved. The small speculum,
being a plane mirror placed at an angle of 45 degrees, may be screwed nearer
the great speculum, for the picture or image to be formed withoutside the
tube, so that there may be room for the head of the viewer between the small.
plain mirror and a concave of short focus, say two inches radius, and three
quarters of an inch diameter, or more, the great speculum being about six
inches diameter, and ten foot radius. The image will be seen about sixty
times magnified; but the small concave speculum must be placed at a small,
angle for the viewer, and a smaller concave speculum may be used, say of one
inch radius, or less, the object inverted, and sides inverted.
Variation. But a plane mirror of small diameter placed to reflect the rays
back towards the side of the hole in the tube (where they came through from
the plane mirror at angle 45 degrees), and the small concave mirror, of
whatever small focus, placed near the edge of the hole of the great tube, with
its back part towards the tube, and adjusted at a small angle for the viewer, as
well as the outer small plane mirror being adjusted at its proper tho' small
angle, and now the internal plain mirror adjusted by its screw, &c., the object
will appear as with the old construction (with one eyeglass) inverted.
Variation second.- Instead of the outside plane mirror, a convex mirror of
less than inch diameter (and radius double or much greater than double the
small concave), placed in the room of the plane mirror, and the internal plain
speculum again adjusted, the magnifying power is encreased, there being but
one image; and the convex speculum will be a means for the eye station to
be farther off the small concave speculum, which is an advantage to the
viewer. The convex speculum need not be so great diameter as the concave,
except its distance from concave is great, because the picture of the sun,
formed from a concave of ten foot radius, is but about five tenths of an inch
diameter, and few telescopes that magnify much will shew the whole disc of
either the sun or moon (at the same instant), tho' that degree of magnifying
power ought perhaps to be the least.
Variation third. The outside speculums may be both concaves, the eye
speculum to be at less distance than the principal focus of the third speculum.
The variations, all by reflection, may be extended farther, agreeable to the
plan, either by reflecting the light from a convex speculum to pass by and on
the other side the internal plane speculum, and to be received by a larger
concave for viewing; or the image may form a second time between two

page_text: concaves; or a concave or convex may be the third speculum, to reflect the
light back on internal plane speculum, and from thence to another plane
speculum at same angle, by great speculum, to be viewed on the side
by reflection or refraction, &c.
Refraction improvement.-If one eyeglass is generally made use of, yet a
second may be used, with advantage of magnifying power, and a concave form,
suppose of double the radius of the convex glass, and about its own radius
distance from the convex eyeglass. Adjust the small speculum, and if greater
degree of magnifying power is yet desirable, the concave glass may be placed
farther off from the convex. If two plane convex eyeglasses are used, have
placed the smallest focus and convex side nearest the image, and the longest
focus and convex side near, and every near, the eye. If distant print or
writing is desirable to be read without appearing inverted, the telescope may
be altered one fourth of a round, for the eye-piece tube to be upright, conse-
quently the viewer to look downward, and back toward the real object (if seen
by refraction).
Refracting telescopes improved.-About the year 1759 or 1760, Hugh
Dixon combined to a two-foot object glass a concave glass of a little greater
radius, and found the focus then to be about seventeen foot. What are called
achromatic telescopes are made upon the plan since that time, though with less
acquired length of focus, and the eyeglasses different in number (and situa-
tion in some respect). But the great length of the telescope or tube is readily
dispensed with upon the new plan, by fixing either a plane mirror, or convex,
or concave, if of a long radius, about the distance of half the length of the old
tube, but say at the end of the new tube, unless the viewer chooses to be
stationed about the middle of the telescope, instead of the object end, &c.
But to describe the station near object end :-The plain, or convex, or long
radius concave speculum, placed at about half the distance of the focus of the
object glass or glasses, and at a small angle for reflecting the light, to form the
image of the object in or near the principal focus of a concave mirror placed
at the object end. When adjusted, the image is seen inverted.
But enough has been said of the plan to rectify the image, and many varia-
tions. The metal speculum for vision gives an advantage of field of view,
and by its form corrects the error of refraction, in my opinion.
Solar microscope on the plan.-A small concave mirror, diameter and focus
at pleasure, a small hole through the middle, widest at the back part; in the
hole, but near the polished surface, a concave glass, to cause the accumulated
light to fall on the object with either a small degree converging or paralel
or diverging manner; the objects being small, and on a small circular piece of

page_text: black body, supported by a narrow bit of metal or flatted wire, very little of
the light will be obstructed which should help to form the image. The object
screwed until between the center of cavity and principal focus of the concave
speculum, the picture would be formed at a distance according, and behind the
real object. But to extend the magnifying power (or diverging of the image),
and if the room is short, to answer the purpose of a longer room, add a large
diameter speculum, form convex, and radius rather long; adjust the object's
distance, and receive the picture on a white concave surface on one side, or
beyond the object place or around it. A plane mirror may be used instead
of convex for throwing the image to side of room, &c., or one person may view
the image from a concave mirror of large diameter. It is needless mentioning
the use of a concave glass instead of the convex or plain mirror while vision is
desirable by reflection.
Visuals and spectacles.-Two thin and concave speculums, radius about four
inches or more, an hole through the center of each, and of about two tenths of
an inch diameter; these fixed one for each eye in a frame, as for spectacles, and
two convex metal speculums of about two tenths of an incli diameter, more or
less, and radius from between 3 and 6 inches, or according as to assist the sight
of them who need magnifying or diminishing the objects. One of these placed
each opposite the hole of the concaves, and adjusted by a screw &c., supported
by a narrow and thin metal or wire, the object's image will be seen without
glass, and suited to any age; the same metals being capable of adjusting for
different persons; and the set for one eye could be used for the Newtonian
telescope, if the proper focus virtual is given to the convex; and a small
hole may be made through center of the convex for viewing, tho' a very
small piece of opake matter be placed at some distance direct before that
hole. Glasses for vision or spectacles with concave and convex glasses to
move nearer or farther off each other, to suit either young, middle age, or
old persons with the same spectacles, if consisting of only of two glasses for
cach eye, the plane convex glasses to be nearest the eyes, and focus two inches,
and the concaves farthest from the eyes, and focus about two inches and one
tenth, and of a tenth of an inch virtual, the convex and concave surfaces
placed very near together; and if both are of flint glass the compound focus
will be about 41 inches; if crown green glass, and worked on same tools, about
33 inches; if Dutch white, focus about 81 and inches; but the flint convex
and Dutch white concave, quite close together, act as a long virtual focus con-
cave, yet at about three tenths of an inch distance have a positive focus of
about 30 inches, and at about half an inch asunder a focus of ten inches;
but the before-mentioned glasses at half an inch asunder, the focus about 7

page_text: and 5, and six inches which shews that any age may be suited by removing
the distance of the glasses according; and if the concaves are double concave
there must be another plane convex glass to each to cause the like effect, and
then the spectacles may seem as if all plain glass. A large concave speculum,
radius 16 or 18 or 20 inches, placed face downward, framework to support it,
and plane mirror under face upward, will do to assist in reading small print with
both eyes; but if plane mirror placed at angle of 45 degrees, and a small hole
through its center, objects one one side may be viewed; but if that plane mirror
be small, and placed as a Newtonian telescope, with a concave glass above
and a ground but unpolished glass plane or meniscus or part of a large sphere
of equal thickness, the picture of objects near would be delineated. Refracting
telescopes, improved by shortening, and viewing by reflection, if of small
magnifying power, as the field of view would be very large, would well suit for
determining the distance of a known sized object, if the object glass or glasses
were to screw to adjust the place for distant vision, the viewer first fixing his
point for the distinct view of the moon or heavenly bodies, or distant land
objects, if they differ sensibly on the scale of even 10 rounds of so large a
screw to an inch, then by adjusting the scale to the age of the eye the varia-
tion of parts of a turn or whole turn of screw afterward for a different object
may shew its real distance somewhat near, or be of use possibly at sea.
In witness whereof, I, the said Hugh Dixon, have hereunto set my hand
and seal, this Thirteenth day of January, One thousand seven hundred
Inrolled the Thirteenth day of January, in the year of our Lord One
thousand seven hundred and eighty-six.