AN IMPROVED INSTRUMENT FOR MEASURING DISTANCES
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
I ALEXANDER MELVILLE CLARK of the firm of A. M. and Wm Clark of
53 Chancery Lane in the County of Middlesex, Fellow of the Institute of Patent
Agents, do hereby declare the nature of the said invention for "AN IMPROVED
INSTRUMENT FOR MEASURING DISTANCES," (a communication to me from abroad by
the firm of Dany and Lepage of Paris, France) to be as follows:-
This Invention relates to an improved instrument for measuring distances,
whereby the indication of the distance of the object observed from the station
is obtained immediately by a simple motion of the alidades without measuring
a base line or the angles made by the relative displacement of the sights or
telescopes.
In principle the instrument consists of a frame mounted on a ball and socket
joint so as to be capable of motion about this joint in different planes and carrying
at the lower part a fixed telescope or pair of sights and a second telescope or pair of
sights inounted above the first and pivoted so as to be moveable in the vertical plane.
The greater or less angles made by these two telescopes or pairs of sights correspond
to the different distances of the station from the object sighted and by this greater
or less opening of the angle made by the sights, telescopes or alidades, a needle is
cause to traverse over a graduated limb. As the position of the needle corresponds
to greater or less angles which themselves correspond to different distances it will
be understood that the scale having been graduated once for all by actual experiment,
all that is necessary after having sighted the object first through the fixed telescope
or sights and then without changing the position of the instrument through the
inovable one, is to read off the figure indicated by the needle on the graduated
limb, in order to know exactly the distance it is desired to measure.
In order that the Invention may be more readily understood I have illustrated
examples of the instrument in the annexed drawings and will proceed to describe
it in detail with reference thereto.
Figure 1 represents in an elementary way a front elevation of the instrument.
Figure 2 a plan of the base of the frame. Figure 3 is a face view of the upright
to which the movable telescope is pivoted by one end and Figure 4 is a face view
of the other upright showing the adjustment for the free ends of the movable

page_text: telescope. a is a bar mounted on a ball and socket joint on a foot b. c and g. are
two uprights rising from the ends of the bar a. d is the fixed sight tube or
telescope secured to the uprights c and g and ƒ is the movable sight tube or telescope
pivoted at one end on centres e in the upright e and supported at its other and
movable end by a seat k on the point of an adjusting screw i screwed through a
nut h on the upright g by means of a nutted head j. is a friction pinion on an
axis mounted in bearings in the frame g and rotated by frictional contact with a
sector o fixed on the movable telescope or sight tube f and m is a needle fixed on
the axis of said pinion and moving over a graduated limb n. A vernier may be
applied to the graduated limb if necessary for reading fractional divisions.
I do not however limit myself to the above described elementary construction
and arrangement of the instrument, but amongst other possible modifications it
may be constructed as represented in Figures and 6 whereby the indications are
rendered more sensible and the instrument is made susceptible of more general
application to the different geodesical operations to which it may be necessary to
have recourse. As will be seen by these figures, the instrument is mounted on a
geodesical circle a and the circular graduated limb b is therefore horizontal when in
its normal position and the needle is replaced by an alidade c whose extremity is
provided with an index which corresponds with the divisions of the graduated limb b
and which is moved automatically by a maltese cross wheel & through the medium of
a small rod e; the wheel d has as many notches as the limb b has circles of division.
The instrument is provided with two telescopes, one f fixed and the other g
movable;
the latter is adjusted by turning a spindle h geared by pinions with a
tangent screw i engaging with a worm wheel on whose axis is fixed a pinion m
which gears with a toothed sector n pivoted at o whose position is capable of
adjustment. The heel p of the sector n is toothed and gears with a rack g carrying
an index which shows on a scale the number of turns of the alidade adjustment.
This mechanism is mounted on a ring or plate s mounted between the geodesical
circle a and the graduated limb b.
To obtain a quick return motion of the alidade to its initial position, the tangent
screw i is mounted on a support which allows of the screw being engaged or
disengaged at will from the wheel 7 by turning the screw u.
The teeth of the different pinions and racks of the instrument are of little
depth, being in fact little more than milling, and to. ensure their constant engage-
ment and adjust for wear, it is only necessary to turn one or other of the tightening
screws v.
A plumb line is attached at any convenient point beneath the supporting plate
of the instrument.
The principle and operation of the instrument remain the same as before and
with the instrument thus constructed I may combine a vertical sector or limb for
measuring altitudes.

page_text: I, ALEXANDER MELVILLE CLARK, of the firm of A. M. and Wm. Clark, of
53, Chancery Lane, in the County of Middlesex, Fellow of the Institute of
Patent Agents, do hereby declare the nature of the said Invention for "AN
IMPROVED INSTRUMENT FOR MEASURING DISTANCES" (a communication to me from
abroad by the firm of Dany and Lepage of Paris, France,) and in what manner the
same is to be performed, to be particularly described and ascertained in and by.
the following statement:-
This Invention relates to an improved instrument for measuring distances,"
whereby the indication of the distance of the object observed from the station
is obtained immediately by a simple motion of the alidades without measuring
a base line or the angles opened by the relative motion of the sights or telescopes.
In principle the instrument consists of a frame mounted on a ball and socket.
universal joint so as to be capable of motion about this joint in any plane, and
carrying at the lower part a fixed telescope or pair of sights and a second telescope
or pair of sights mounted above the first and pivoted so as to be moveable in the
vertical plane. The greater or less angles made by these two telescopes &c.
correspond to the different distances of the station from the object sighted and
by this greater or less opening of the angle made by the sights, telescopes or
alidades, a needle is caused to traverse over a graduated limb. As the position of
the needle corresponds to greater or less angles which themselves correspond to
different distances it will be understood that the scale having been graduated once
for all by actual experiment, all that is necessary after having sighted the object.
first through the fixed telescope or sights and then without changing the position
of the instrument through the movable one, is to read off the figure indicated by
the needle on the graduated limb, in order to know exactly the distance it is.
desired to measure.
In order that the invention may be more readily understood I have illustrated
examples of the instrument in the annexed drawings and will proceed to describe
it in detail with reference thereto.
Figure 1 represents in an elementary way a front elevation of the instrument.
Figure 2 a plan of the base of the frame. Figure 3 is a face view of the upright
to which the movable telescope is pivoted by one end and Figure 4 is a face view
of the other upright showing the adjustment for the free end of the movable
telescope. a is a base plate or bar mounted on a ball and socket joint, on a foot b.
c and g are two uprights rising from the ends of the bar a. d is the fixed sight
tube or telescope secured to the uprights c and g, and f is the movable sight tube
or telescope pivoted at one end on centres e in the upright c and supported at its
other and movable end by a seat k on the point of an adjusting screw i screwed
through a nut h on the upright g by means of a milled heal j. is a friction
pinion on an axis mounted in bearings in the frame g and rotated by frictional
contact with a sector o fixed on the movable telescope or sight tube f, and m is a
needle fixed on the axis of said pinion and moving over a graduated limb n.
A vernier may be applied to the graduated limb, if necessary for reading fractional
divisions.
I do not however limit myself to the above described elementary construction
and arrangement of the instrument, but amongst other possible modifications it
may be constructed as represented in Figures 5 and 6 whereby the indications are
rendered more sensible and the instrument is made susceptible of more general
application to the different geodesical operations to which it may be necessary to

page_text: have recourse.
As will be seen by these figures, the instrument is mounted on a
geodesical circle a and the circular graduated limb b is therefore horizontal when
in its normal position and the needle is replaced by an alidade c whose extremity.
is provided with an index which corresponds with the divisions of the graduated
circle 6 and which is moved automatically by a maltese cross wheel d through the
-medium of a small rod e; the wheel d has as many notches as the limb b has
circles of division.
The instrument is provided with two telescopes, one ƒ fixed and the other g
movable; the latter is adjusted by turning a spindle h geared by pinions k with a
tangent screw i engaging with a worm wheel on whose axis is fixed a pinion m
which gears with a toothed sector n pivoted at o whose position is capable of
adjustment. The heel p of the sector n is toothed and gears with a rack g carrying
an index which shows on a scale the number of turus of the alidade adjustment.
This mechanism is mounted on a ring or plate s mounted between the geodesical
circle a and the graduated circle b.
To obtain a quick return motion of the alidade to its initial position, the tangent
screw is mounted on a support which allows of the screw. being engaged or.
disengaged at will from the wheel by turning the screw u.
The teeth of the different pinions and racks of the instrument are of little
depth, being in fact little more than milling, and to ensure their constant engage-
ment and adjust for wear, it is only necessary to turn one or other of the tightening
screws v.
A plumb line is attached at any convenient point beneath the supporting plate
of the instrument.
The principle and operation of the instrument remain the same as before and
with the instrument thus constructed I may combine a vertical sector or limb for
measuring altitudes.
The modification represented in figures 7, 8, and 9 relates chiefly to the mechanism
for adjusting the movable telescope and to the mode of indicating the distances
observed. Figure 7 shows a plan of the mechanism, the graduated circle and the
two telescopes being removed the positions of the latter being merely indicated by
their centre lines. Figure 8 is a plan of the complete instrument and figure 9 is a
section on line 1-2 figure 8. In these three figures the same reference letters
indicate the same parts and it will be sufficient to explain the operation of the
modified instrument to enable the improvements to be readily understood. The
instrument is mounted on a suitable foot or other support whereby it may be
adjusted in any desired plane and there fixed as are most geodesical instruments.
The point of which the distance is required to be ascertained is first sighted by
means of telescope a after having previously ascertained that the axes of the two
telescopes ab are perfectly parallel which is denoted by the index aṛm.c bearing
close against the stud d on the graduated circle, at the commencement of the
operation if the instrument is properly regulated. Then by turning the centre
button e whose axis is in gear through a train of wheels and pinions n with a
toothed sector o attached to the movable telescope b, the said telescope is turned
on as a centre and quickly brought approximately into line with the point to be
sighted and then (after having verified that this point is still in the axis of the fixed
telescope) the tangent screw g is thrown into gear with the pinion on the axis of
wheel e and by means of this tangent screw actuated by the button h the movable
telescope is accurately adjusted to the required point. The distance.sought may
then be read off directly on the graduated circle i by the index c.
The tangent
screw g is thrown out of gear, to permit of the movable telescope being quickly
adjusted roughly or returned to its parallel position, by means of a cam which is
turned by a button and acts on a lug m projecting from the movable bearing
in which the spindle of the tangent screw is mounted. Thus constructed the
mechanism is strong and reliable and does not project appreciably from the
perimeter of the instrument which may be constructed of any desired dimensions
aud arranged as a pocket instrument for military and tourists' use.

page_text: To shorten the index c at each revolution to the radius of the corresponding
circle of graduations the index is made in two parts sliding the one on the other
and provided with a rack of teeth on the under side which engages with a flat
helix on a fixed plate p.
f.
The graduated circle and the index may be replaced by a drum graduated
helically and actuated by a knob r on the end of its spindle as shown in.
dotted lines in ligure 7, but the arrangement of the drum may be modified"
according to circumstances. The fixed collar bearing in which the drum turns is
provided witli an aperture through which may be seen the figure indicating the
distance measured. The gearing for transmitting motion from the drum to the
movable telescope is similar to that already described.
Each telescope tube may be provided with a chamber containing a mirror inclined
at an angle, these two chambers being connected by a tube having universal joints..
The apparatus may also be provided with an arrangement whereby the angles may
be read off at same time as the distances, and if desired a recording device for
obtaining record of the numerical and graphical indications furnished by the
instrument.
Having now particularly described and ascertained the nature of the said
Invention and in what manner the same is to be performed I declare that what
I claim is
1st In an apparatus for the automatic measurement of distances, the arrangement
of mechanism whereby motion is given to the movable telescope or sight tube g
and consisting essentially of a toothed sector n in gear with a wheel 7 and the
tangent screw i for actuating wheel and capable of being thrown in and out
of gear therewith, substantially as described with reference to figures 5 and 6 of
the drawings.
2nd In an apparatus for the automatic measurement of distances, the mechanism
for actuating the index sliding in the arm c in order to indicate the distances on
the graduated circle, and consisting of a wheel & gearing with a pinion fixed on
the axis of the wheel and a rod e fixed to the index, as and for the purpose
specified.
.
3rd The mechanism for indicating the number of revolutions made over the
graduated circle and consisting of a rack g actuated by the toothed heel of the
sector n, the rod q sliding on the fixed part of which each division indicates one
revolution as described in reference to figures 5 and 6.
4th In an apparatus for the automatic measurement of distances the mechanism
for adjusting the moveable telescope b on its centre f, consisting of the train
and the toothed sector o actuated from the centre axis, substantially as described
in reference to figures 7 to 9.
5th The combination of the telescopically sliding rack toothed index c with the
stationary flat worm p for indicating the distances corresponding to the number of
revolutions made upon different circles of the graduated limb i as described with
reference to figures 8 and 9.