Improvements in Range-finding or Distance-measuring Instruments.
Year: 1888

page_text: Date of Application, 20th July, 1888
Complete Specification Left, 9th Apr., 1889-Accepted, 20th July, 1889
PROVISIONAL SPECIFICATION.
Improvements in Range-finding or Distance-measuring Instruments.
I, THOMAS BOLTON, of 9 Park Street, in the city of Calcutta, in the province of
Bengal, India, Director of the Government Mathematical Instrument Department,
Calcutta do hereby declare the nature of this invention to be as follows:-
It consists essentially of the following parts--A sufficiently rigid base bar a few
feet in length is supported by one or two portable tripods-At each end of the bar
are two telescopes firmly fixed together with their optic axes at right angles to one
another, or very nearly so-Each couple of telescopes is provided with a small
amount of horizontal and vertical adjustment-That telescope of each couple, which
lies with its optic axis at right-angles to the base bar, is used for sighting the object
whose distance is required-These two telescopes are provided with cross lines, the
point of intersection of which marks out the centre of collimation of each telescope-
Both are provided with focussing arrangement-The other two telescopes lie parallel
to the base bar, with their object glasses towards one another, so that they look
directly into one another-We will call these two telescopes, collimators, that one at
the right hand end of the bar, Collimator No. 1-and that one on the left end-
Collimator No. 2-Each of these Collimators has its cross lines permanently fixed in
its principal focus with their intersection point exactly at the centre of collimation-
and focussing is dispensed with-These cross lines consist of one principal vertical
line crossed by a subsidiary horizontal line-The vertical line of each collimator is
set exactly at right angles to the line of collimation or optic axis of the observing
telescope affixed to it-Behind the cross lines of collimator No. 1, and on that side
of them remote from the object glass, is a piece of opal glass, or other light scattering
substance, which will, when illuminated by the daylight, afford a uniformly illuminated
background, against which the cross lines will appear black-The similar cross lines
in collimator No. 2, are viewed through a positive eyepiece, which is attached to the
micrometer-If now, the two observing telescopes, separated by the length of the
base bar, be directed towards, and focussed upon the object whose distance is required,
so that precisely the same point of the image of the object is caused to fall, by means
of the adjustments, upon the intersection point of the cross lines, then collimator No. 1
will cast light, proceeding from its focus, into the object glass of collimator No. 2,
which will bring that light again to a focus, and an optical image of the cross lines
of collimator No. 1 will be formed in the same plane and focal area as the real cross-
lines of collimator No. 2-Collimator No. 2 is provided with slight vertical adjustment,
whereby it can be tilted, so that the intersection point of the cross-lines of collimator
No. 1 (seen in image) may fall nicely upon the horizontal line of Collimator No. 2-
The two collimators and their cross lines are so fixed and adjusted with regard to the
observing telescopes, that if the two latter are directed and focussed carefully upon
an object at a practically infinite distance, such as a star, (whose image is nicely
bisected by the cross lines) then the optical image of the cross-lines of collimator No. 1,
shall fall exactly upon, and coincide with the real cross lines of collimator No. 2, or,
in other words, when the axes of collimation of the two telescopes lie exactly
parallel to one another, then the axes of collimation of the two collimators are.
likewise exactly parallel, though not necessarily in the same straight line-If the
object, whose range is required, is situated at a distance say within 4 miles, so as to
present an appreciable parallax, then it is evident that the observing telescopes must
converge more or less in order to properly sight the same point of the object, & thus
he optical image of the cross line of collimator No. 1, no longer falls exactly upon,
and coincides with the real cross line of collimator No. 2, but a separation is
perceptible, the amount of which is a measure of the parallax or the angle subtended

page_text: by the distance between the two telescopes if it be viewed from the position of the
object The office of the micrometer mentioned above is to measure the space
separating the fixed vertical line and the image-Besides the fixed vertical line in the
focus of collimator No. 2, there is a moveable cross line, which can be caused to
travel in a direction perpendicular to the length of the fixed vertical line, by means
of a fine screw having a convenient number of threads to the inch-The screw
possesses a graduated head, and provision is made for registering the number of
revolutions of the screw-This moveable cross line lies as closely as possible in the
same plane as the fixed cross-lines, and when the intersection point of the micrometer
lines lies exactly upon the fixed vertical line, the reading of the micrometer is
theoretically, infinity-In taking an observation, the number of revolutions and
fractions of revolutions of the micrometer screw necessary to move the intersecting
point of the micrometer lines from coincidence with the fixed vertical line to
coincidence with the image of the vertical line of collimator No. 1, will either directly
or indirectly, according to the method of graduation adopted, shew the real distanco
of the object from the instrument.
THOMAS BOLTON.
COMPLETE SPECIFICATION.
Improvements in Range-finding or Distance-measuring Instruments.
I, THOMAS BOLTON, of 9 Park Street, in the city of Calcutta, in the province of
Bengal, India, Director of the Government Mathematical Instrument Department,
Calcutta, at present residing at 8 Carlton Terrace, St. Martin's Square, Scarboro'
do hereby declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
This invention which relates to range-finders or distance measuring instruments
will be best understood by reference to the accompanying drawings in which
figures I and I are two parts of a plan of an instrument constructed according to
my said invention the cover being removed the better to show my improvements:
figure 2 is a view showing one of the telescopes or collimators in elevation and the
carrier on which it is mounted in section; Figure 3 is a plan drawn to a smaller
scale showing the instrument complete but with portions of the cover removed.
Figures 4 to 7 are diagrams illustrating the working of the instrument.
in
With reference to figures 1 to 3, B B B is the base bar which for general
purposes measures six feet or so in length from C to C. I here show the base bar
a hollow or box forming one piece with the two crossed parts B₁ B¹, the
whole enclosing the telescopes and thus protecting them from injury. Doors are
provided wherever necessary, to enable the observer to get at the various parts of
the instrument. This base bar may be supported upon one firm and portable tripod
stand under its middle, or upon two such, one under each end; the former method
being as a rule the most convenient.
Two cylindrical fittings or centres C and C are fixed to or inside the base bar
and at a distance apart from centre to centre equal to whatever length of base has
been chosen as a basis for calculating the distances of remote objects.
One of these fixed centres is shown in section at C in figure II. A carrier R R
(Fig. 2) turns upon each centre C and is adjustable in a horizontal plane by
means of the adjusting screw S working through a cock-piece fixed to base-bar. The
end of each carrier R R is kept up against end of screw S by means of a counter
spring.
The two telescopes T T¹ and T' T' respectively are attached to their carriers R R
by means of the horizontal hinges AA and A¹ A¹. Thus if the carriers are rotated
about their centres C they must carry their telescopes round with them, while at the
same time each telescope may be tilted in a vertical plane, independently of the
horizontal motion of the carrier. This tilting is effected by means of screw S¹

page_text: (Fig. 2) which is tapped through the end of carrier R R and bears up against the
telescope. This vertical motion combined with the horizontal motion of the carriers
enables the observer to direct the two observing telescopes T T¹ and T² T³ upon the
same point of a distant object with the greatest precision; they being provided at
their eye
ends with a point or cross line with which the image of a selected point of
object is brought into coincidence by means of the adjustments and focussing screw.
In this invention I call the two telescopes "crossed telescopes" because the body of
each of the two observing telescopes T T and T T³ forms one piece with the body
of another telescope, (L L and L L respectively) fixed across it so that the optic
axis of each pair intersect at about a right angle. Those two telescopes which thus
object glass
look into one another I call "collimators." Collimator L L' carries an
at L and just at the parallel focal point of the object glass, at end I is fixed a
sharply definite point, or a pair of fine crossed lines forming a definite point at their
intersection or any arrangement of spider lines, or lines ruled upon glass, or apertures
of any form cut out in opaque sheet metal in such a way as to sharply define some
one particular point at the focus and on the optical axis of the collimator L L'.
Behind this point, which I call the "collimation point" is placed a piece of ground
or opal glass to form a luminous back-ground to the collimation point. When the
instrument is in use this piece of ground glass is illuminated by day-light falling
upon it when the end of the base-bar is thrown open behind it. The collimator L' L
forming part of the other crossed telescope has its object glass at L' directed towards
observing
object glass of collimator L L¹. I call this collimator I L³ the
collimator" because at its eye-end L'is fixed a micrometer and drum whereby the
distances of objects being observed by the instrument are read off directly. It will
be well known to those acquainted with practical optics that if the two collimators LL
and L L are looking directly into one another with their optic axes exactly parallel
though not necessarily coincident, then the two object glasses will cause an optical
image
of the collimation point at L to be formed on the optical axis and in the
parallel focal plane of the collimator L' L³ that is at the point marked by a cross
near L. This end of the observing collimator is provided with a micrometer
consisting, but not essentially, of a slide working backwards and forwards in a
direction perpendicular to optical axis of L'L'. The slide of micrometer carries a
pair of fine lines or it
very accurately defined point formed by the intersection of a
may be only one line provided it is placed accurately perpendicular to the direction
of movement. This point is of course placed nicely in the plane in which the image
of the collimation point in collimator L L' comes to focus, so that by means of the
eye-piece E this image may be clearly seen together with, and at the same time as the
real line, lines, or point in the micrometer.
The reading drum D D is spirally grooved and is embraced by a ring which fits
into the grooves. This ring is provided at a convenient point with a reading mark.
When the drum is rotated it causes the ring (which cannot rotate) to travel back-
wards or forwards along the drum, and thus the reading mark is caused to follow
along the elevated spiral, and to point successively to the different figures engraved
thereon. This drum forms the head of a screw of fine and accurate pitch which in
3 rotating, causes the slide in the micrometer to travel backwards and forwards.
The action of the instrument is as follows;-
Suppose a base of 6 feet is adopted, then distance CC is exactly six feet. In first
place let the two observing telescopes T T and T3 T3 be both directed upon exactly
the same point of an object situated at the greatest distance say 6000 yards which
the instrument is designed to measure. Then the optical axes of the two observing
telescopes will not be exactly parallel but will converge slightly towards object.
The result is that the image of cross line at L will fall at La trifle more towards the
drum than it would do were the observing telescopes exactly parallel.-
Let the reading point (or cross line) in the micrometer slide be made to coincide
exactly with the image thrown from the other collimator and that being done, cause
the reading point on the ring to fall upon the proper end of the spiral where a mark
is made for 6000 yards. Again if the two observing telescopes are directed, as

page_text: before, upon a much nearer object then the amount of convergence between their
optical axes will be increased more or less, and the consequence is that the image of
the collimation point cast into the observing collimator is thrown still more towards
the drum, and therefore the latter must be rotated in order to bring the cross line
of the micrometer again into coincidence with the image of collimation point.
Therefore the reading point of the ring must have travelled to a point farther along
the spiral, and so the nearer the object towards which the observing telescopes are
made to converge, the farther down the drum will the ring have to travel before the
cross line of the micrometer can be brought into coincidence with the image of the
collimation point. Thus the same distance will always imply the same reading on the
drum and in practise I havo the real distances engraved upon the spiral of the drum
either by trial upon the actual distances or by other methods equally trust-worthy.
Therefore, whenever the distance of a remote object has to be found by means of
my invention, the instrument is put upon its tripod, and the telescopes are then
brought to bear upon the distance object, and a particular point thereof selected for
sighting upon, and the image of such select point of object is brought into coincidence
with the point or cross line in the eye-end of each telescope, by means of the
adjustments, then the observer goes to the micrometer and rotates the drum until the
cross line is brought into exact coincidence with the image of collimation point and
then the reading on the drum or the figure to which the mark upon the ring points,
is the distance required in feet or yards or whatever other units of measurement are
required.
In figure 4 the collimators T T¹, T' T³ being parallel and the micrometer in its
zero position the object glasses for the axis upon which the rays bend it being
understood that the rays between the two object glasses are always parallel and
converge from the said object glasses to the focus point according to the position or
angle of the object glass.
In figure 5 the collimator T2 T3 is at right angles and the collimator T T¹ is
turned in at an angle some of the rays passing from one to the other object glass
being lost while the other rays converge to the focus point the micrometer being
here shown as adjusted to the said focus point.
In figure 6 each of the collimators is turned in at a like angle and as in figure 5
some of the rays are lost while others converge to the focus point.
In figure 7 each of the collimators is turned in at an angle which does not permit
of any of the rays falling on the object glass at L³ reaching the before-mentioned
focus point so that no observation can be taken this representing a position for
measuring the distance from an object within the minimum limit of the instrument.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is ;-
1. The use of two crossed telescopes separated by a definite distance on a hase
bar, one telescope of each pair for sighting the distant object and the other two
looking into one another, and by virtue of their construction described above, causing
the amount of convergence of the observing telescopes to be rendered measurable by
the lateral variation in the position of an image.
2. The use of the drum D D attached to a fine screw for bringing the real cross-
line into exact coincidence with the moveable image of the collimation point, and so
graduated that the variations of the position of that image are read off directly in
terms of the actual distances which correspond to those variations of the image.
D
11 1
THOMAS BOLTON.
W. P. Thompson & Boult,
Agents for the Applicant."