IMPROVEMENTS IN MEASURING INSTRUMENTS
Year: 1855

page_text: LETTERS PATENT to John Imray, Engineer, of 64, Bridge Road,
Lambeth, Surrey, for the Invention of "IMPROVEMENTS IN MEASURING
INSTRUMENTS."
Sealed the 31st July 1855, and dated the 5th February 1855.
PROVISIONAL SPECIFICATION left by the said John Imray at the
Office of the Commissioners of Patents, with his Petition, on the
5th February 1855.
I, JOHN IMRAY, Engineer, of 64, Bridge Road, Lambeth, Surry,, do
hereby declare the nature of the Invention for "IMPROVEMENTS IN MEASURING
INSTRUMENTS" to be as follows:- .
My improvements consist of apparatus by which the distance of a visible
object may be ascertained. A mirror, partly unsilvered, and an eye-piece or
telescope, are fixed on a frame, so that the line of sight shall cut the plane
cf the mirror at an angle of 45°. From the frame, at right angles to the line of
sight, an arm projects, on which another mirror is mounted so as to slide in a
straight line to or from the fixed mirror. The inclination of the sliding mirror
is adjusted, so that when it is at a particular point of the arm, an observer
looking through the eye-piece or telescope shall see a distant object partly
through the unsilvered portion of the fixed mirror, and partly reflected from
the sliding mirror to the fixed mirror, and thence to the eye, the two images
being apparently coincident. Retaining the same inclination of the mirrors,
on looking to an object at a different distance, in order that the direct and
reflected images may be made to coincide, the sliding mirror has to be moved
to or from the fixed mirror, according as the second object is at less or greater

page_text: distance than the first, the distances between the mirrors being exactly pro-
portional to the distances of the objects from the fixed mirror. The arm on
which the mirror slides is graduated in any convenient number of divisions,
and the inclination of the mirror is adjusted so as to make this graduation any
suitable scale of distance, as, for instance, an inch on the arm reckoning for one
hundred yards of distance of an observed object; and the instrument being thus
properly adjusted for one or more known distances, is fitted for measuring any
other distances not exceeding the range of its scale.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said John Imray in the Great Seal Patent Office on the
4th August 1855.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
IMRAY, Engineer, of 64, Bridge Road, Lambeth, Surrey, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fifth-day.. of. February, in the year of our
Lord One thousand eight hundred and fifty-five, in the eighteenth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said John Imray, Her special licence that I, the said John
Imray, my executors, administrators, and assigns, or such others as 1,
the said John Imray, 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 "IM-
PROVEMENTS IN MEASURING INSTRUMENTS," upon the condition (amongst
others) that I, the said John Imray, by an instrument in writing under
my hand and seal, should particularly describe and ascertain the nature of
the said Invention, 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.
NOW KNOW YE, that I, the said John Imray, do hereby declare the
nature of the said Invention, and in what manner the same is to he per-
formed, to be particularly described and ascertained in and by the following
statement thereof, that is to say:-
My improvements consist of apparatus by which the distance of a visible

page_text: object may be ascertained: A mirror; partly unsilvered; and. an eye-piece.or
telescope, are fixed on a frame, so that the line of sight shall cut, the plane
of the mirror at an angle of 45°. From the frame, at right angles to the line of
sight, an arm projects, on which another mirror is mounted, so as to slide in: a
straight line to or from the fixed mirror. The inclination of the sliding mirror
is adjusted, so that when it is at a particular point, of the arm, an observer
looking through the eye-piece: or telescope, shall see a distant object partly
through the unsilvered. portion of the fixed mirror; and partly reflected from
the sliding mirror to the fixed mirror, and thence to the eye, the two images
being apparently coincident.. Retaining the same inclination of the mirror, on
looking to an object at a different distance, in order that.the.direct and reflected
images may be made to coincide, the sliding mirror. has to be moved to or from
the fixed mirror, according as the second object is at less or greater distance
than the first, the distances between the mirrors being exactly proportional to the
distances of the objects from the fixed mirror. The arm. on which the mirror
slides is graduated in any convenient number of divisions, and the inclination
of the mirror is adjusted so as to make this graduation any suitable scale of
distance, as, for instance, an inch on the arm reckoning for one hundred yards
of distance of an observed object; and the instrument being thus properly
adjusted for one or more known distances, is fitted for measuring any other
distances not exeeding the range of its scale.
Having thus stated the nature of the Invention, I will proceed to describe
the manner of performing the same.
"
Figure 1 of the annexed Drawing represents a plan of an instrument for
measuring distances made according to my improvements; Figures 2, 3, and 4
are transverse sections, on the lines marked A, A, B, B, and E, K, on Figure 1
respectively; Figure 5 is part of a sectional plan; and Figure 6, part of an
elevation.
a is a triangular bar, whose sides are made accurately plane, one of them
having a scale of equal parts maked upon it; b is an eye-piece or a telescope
fitted at one end of the bar, so that the eye, applied to the aperture at E,
may receive rays of light proceeding in the direction K, E; c is a mirror,
fixed at an angle of 45° to the line K, E, having its lower half silvered, so
as to reflect to the eye at E rays proceeding in the direction G, K, parallel
to the bar a. The upper half of the mirror c is transparent, and there is an
aperture d in its frame, so that rays proceeding in the direction D, K, shall
pass to the eye at E. e is a slide, fitted to two sides of the bar a, against
which it is pressed by a spring f, fixed between the bar and the back of the
slide; a slot is cut in the upper side of the slide, so as to expose part of the

page_text: scale on the bar a, and an index or vernier g is marked on the edge of the slot.
h is a plane mirror fixed on the slide, making an angle greater than 45° with
G, K, a line parallel to the edges of the bar. Both the mirrors c and h are
fitted like those of a sextant, with screws for adjusting them to their proper
inclinations.
If D represent the position of any distant object sending rays in all direc-
tions, some of those proceeding in the direction D, K, pass through the
transparent part of the mirror c to the eye at E, while some of those proceeding
in the direction D, G, and falling on the mirror h, adjusted to the proper angle
for reflecting them in the direction G, K, are reflected from the silvered part
of the mirror c to the eye at E, and thus the direct and reflected images of the.
object at D appear to the observer at E to coincide. In like manner the rays
from an object at F may be made to form coincident, direct, and reflected
images by moving the sliding mirror h along the bar to a position such that
the distance K, HI, shall bear to the distance K, G, the same proportion that
the distance K, F, bears to K, D, as may be demonstrated geometrically. The
mirrors are adjusted to measured distances, so that the lengths indicated by
the scale on the bar are known to represent the numbers of feet, yards, or
other units of measure in the known distances of the objects observed, and then
the distance of any other object observed with the instrument and not beyond
its proper range is indicated on the scale accordingly.
I do not limit myself to the particular form of the bar or its fittings repre-
sented in the Drawing; but I claim as my Invention, a graduated bar, on which
an inclined mirror is mounted so as to slide recticilineally, and another half-
silvered mirror is fixed opposite an eye-piece or telescope, so that when the
inclinations of the mirrors are properly adjusted, the distance of an object from
the fixed mirror is ascertained by moving the sliding mirror along the bar a
proportional distance from the fixed mirror, as determined by the coincidence
of the direct and reflected images of the observed object.
In witness whereof, I, the said John Imray, have hereunto set my hand
and seal, this Twenty-seventh day of July, in the year of our Lord
One thousand eight hundred and fifty-five.
Witness,
ARTHUR COLLINGE.
JOHN IMRAY. (L.S.)