An Improved Topographical Instrument for the Measurement of Angles, Altitudes and Distances.
Year: 1899

page_text: An Improved Topographical Instrument for the Measurement of
Angles, Altitudes and Distances.
PAUL OMER AUBRY, of Vannes, (Morbihan), in the Republic of France,
Engineer, do bereby declare the nature of this invention to be as follows:-
This invention relates to an improved topographical instrument which enables
all the elements necessary for making a topographical survey, to be measured.
This instrument, which is of small dimensions and of very light weight, per-
mits the measurement of angles, distances, heights, hills or angles of elevation.
My instrument comprises:
1. A sextant, the angular displacement of the large mirror of which is con-
trolled in a special manner by means of a micrometer-screw, for the purpose of
being able to easily read off the divisions without requiring the instrument to
be of very large dimensions, or necessitating the employment of a magnifying
glass when these dimensions are very small, as is the case in the so-called pocket-
sextants.
2. A divided rule or scale of special arrangement, permitting the distances to be
found by means of the indicatious obtained from the sextant.
3. A small pendulum combined with a collimator, for the measurement of
angles.
In the accompanying drawing, I have shown, in principle, by way of example
only, my improved instrument.
Figure 1 is a plan of the instrument;
Figure 2 is an elevation; and
Figure 3 an underside view thereof.
Figure 4 is a diagram illustrating the use of my improved instrument.
In these figures, like letters of reference indicate the same parts.
My instrument consists essentially of a sextant comprising, in the ordinary
manner, a small fixed mirror a and a large movable mirror b, but is characterized
by the means for controlling the motion of the latter.
The angular movement of the large mirror is effected, in my improved
instrument, by means of a micrometer-screw c which engages with a toothed
sector d fixed to this mirror b.
An opposing spring e constantly maintains the sector in contact with the
screw e so as to prevent any lost motion.

page_text: The micrometer-screw c bears a head f which enables it to be moved, and
which is divided into a hundred equal parts; this head moves opposite to a vernier
for enabling tenths to be read off.
The plate which is fixed to the toothed sector d, and on which is mounted ibe
large mirror b, bears an index or datum mark which moves opposite to
graduations marked on the table of the instrument, each division corresponding
to one turn of the screw c or of the head f.
The threads of the screw and of the sector d are designed in such a manner
as to give the angle either in centigrades (hundredths), or in milliemes
(thousandths) of the distance.
When the measurement of the angle is to be evaluated in grades, each division
on the table of the instrument corresponds to 10 grades so that the vernier gives
centigrades.
When the measurement of the angle is to be evaluated in milliemes
(thousandths), each division on the table of the instrument corresponds to a
hundred millieumes and the vernier gives the tenth of a millieme.
In order to enable the operator to find the desired distance without having to
make any calculation, the table i bears a divided rule made in two parts between
which parts there moves a slider k operated by means of a pinion engaging with
a rack on this slider A.
The two parts of the said rule, as well as the slider, are provided with
graduated scales.
My instrument renders it possible to employ, for the purpose of measuring the
distance of any point, a method of operation which is quite new and presents
great advantages over all those heretofore employed, since it no longer requires
the operator to move either to right or to left, in order to lay out a base line.
This new method of procedure is as follows:--
Let A, Figure 4, be the point where the operator is stationed, and M be the
point of which it is required to find the distance. The operator commences by
taking a bench-mark R: he then measures, by means of the instrument herein-
before described, the parallax or angle a which the two points M and R subtend
at the point A the operator then moves forward up to the point B, towards the
bench-mark, through a distance which may vary, for example, between from
about 25 to 50 metres, and he then measures the parallax or angle 8 which
the points M and R subtend at the point B.
Knowing the nogles a and 8, one can easily deduce the angle y which is equal to
B-a.
The triangle BA M can then be solved, for one side A B and the two angles a Y
are known. If / be the distance A B, through which the operator advanced,
and r the distance (A M) sought, we have the relation :-
The graduated rule mentioned above, has for its object to give the solution
of this equation directly; for this purpose, the rule proper beurs two series of
logarithmic graduations or scales, one B for distances, the divisions of which
correspond to different values of log. X and of which the graduations give the
value of the distance, the second C for parallaxes or angles, the divisions of which
correspond to the different values of log. sin 3.

page_text: The slider & itself bears a scale 1) with logarithmic graduations, the scale of
differences, the divisions of which correspond to the different values of
log.
Gill (8).
This slider moreover bears a complementury scale E, the scale of base lines,
permitting the operator to vary the longth of the base line 1.
The scales shown in the drawing have been determined on the assumption
that the instrument evaluates the angular measuremonts in grades and centi-
grades.
To sum up, the measurement of the distance of any point is obtained in the
following manner with my instrument:-
1. The operator chooses a bench-mark either to the right or to the left of the
point considered;
He causes, by operating the micrometer-screw, the image of the point to
coincide with the bench-mark, or vice versa.
3. The operator walks in the direction of the bench-mark measuring a base-
line of from 25 to 50 metres.
4. He reads off, on the circular scale A, marked on the table of the instrument,
and on that on the head the divisions before which the two datum-marks h, I
traced, on the one hand, on the sector d, and on the other hand, on the reading
vernier of the head f, come to rest.
5. He again causes the two images of the point considered, to coincide.
6. He reads off as before, the divisions before which the two datum marks h, 1
stop and obtains the difference of the two results.
7. He then moves the slider and brings the division or mark on the scale E,
corresponding to the base-line chosen, opposite to the same division of the
parallax or angle scale C as that of the scale A, before which there is the datum-
mark h.
8. He then reads off, on the scale of distances B, the division which is opposite
the division on the scale of differences D corresponding to the number found for
the difference of the two parallaxes or angles, and the division thus found on
the scale of distances B, gives the desired distance.
My improved instrument offers the great advantage of not requiring any fixed
support; moreover it takes up very little space and is capable of being carried
like a field-glass.
Thus, for example, assume that, with a base 50 metres, the last parallax or
angle found was 560 (in divisions of the head f) as indicated in Figure 1, and
that the difference between the two parallaxes or angles measured was 80, in
divisions of the vernier; in order to find the distance sought, I place the mark 50
on the scale E opposite the division 560 of the scale C and opposite to division 80
of the scale D; I'read off on the scale B, the distance 3200 which is the distance
Fought.
My improved instrument is moreover provided, on the underside of its table,
with a special arrangement for enabling angles of elevation to be mensured.
This arrangement comprises a horizontal cross-wire collimator m, below which
is suspended a pendulum n the free end of which, provided with a vernier o,
moves opposite to a graduated scale giving angles of elevation.
The divisions of this scale F correspond, according to the method of con-
struction of the instrument, either to one grade or to 10 milliemes: the vernier o
of the pendulum n giving tenths, thus enabling altitude to be evaluated either
to 10 centigrades, or to one millieme.
In order to prevent the pendulum from continually oscillating, it is maintained
in its vertical position by means of any suitable spring device which the operator
releases when he wishes to take au observation.
In order to measure an angle of elevation, the operator directs the line of
sight of the collimator m towards the point the height of which is sought; he

page_text: then bears on the small lever so as to release the pendulum n and the division
before which the said pendulum comes to rest, gives the altitude sought.
The sliding scale jk, hereinabove mentioned, also permits the altitude of the
point considered relatively to the point of observation, to be measured.
The operator first measures the angle of elevation, and the distance of this
point as hereinabove mentioned, he then places the division of the scale
of parallaxes or angles (corresponding to the angle of elevation found, opposite
to the division on the scale of distances B corresponding to the distance found,
and the division of the scale of base-lines B which is opposite the division of the
scales of parallaxes or angles C corresponding to an angle of 90 degrees will give
the height sought.
Thus, for example, I assume that the point the altitude of which is desired,
is at a distance of 3200 metres and that the angle of elevation found is equal
to 80 centigrades, I bring the mark 80 of the scale C opposite the distance 3200
on the scale B and I read off on the scale E, 26 metres opposite the division 1000
on the scale of parallaxes or angles C, which division corresponds to a right
angle.
My improved instrument, by reason of the combination of the sextant and the
pendulum-collimator, enables all altitudes to be evaluated, whatever be their
height when the height is too great to be measured directly by the pendulum,
it is only necessary to take a bench-mark near the horizontal, the altitude of this
point is evaluated by means of the pendulum-collimator, then the parallax or
angle of this bench-mark is measured relatively to the point sought; the sum of
the two angles will give the angle of elevation of the point considered and,
consequently, the altitude of this point.
My improved instrument enables all the elements necessary for making a topo-
graphical survey to be measured and is, for this reason, capable of receiving
numerous applications.
It is obvious that I can modify the form, dimensions, and detail arrangements
of my improved instrument according to its various applications.
Dated this 8th day of November 1899.
D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agent for the Applicant.
An Improved Topographical Instrument for the Measurement of
Angles, Altitudes and Distances.
I, PAUL OMER AUBRY, of Vannes, (Morbihan), in the Republic of France,
Engineer, 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 relates to an improved topographical instrument which enables
all the elements necessary for making a topographical survey, to be measured.
This instrument, which is of small dimensions and of very light weight, per-
mits the measurement of angles, distances, heights, hills or angles of elevation.
My instrument comprises
1. A sextant, the angular displacement of the large mirror of which is con-
trolled in a special manner by means of a micrometer-screw, for the purpose of
being able to easily read off the divisions without requiring the instrument to
be of very large dimensions, or necessitating the employment of a magnifying

page_text: glass when these dimensions are very small, as is the case in the so-called pocket-
sextants.
2. A slide rule of special arrangement, permitting the distances to be
found by means of the indications obtained from the sextant.
3. A small pendulum combined with a collimator, for the measurement of
angles of elevation.
In the drawing filed with my Provisional Specification, I have shown in prin-
ciple, by way of example only, my improved instrument.
Figure 1 is a plan of the instrument;
Figure 2 is an elevation; and
Figure 3 an underside view thereof.
Figure 4 is a diagram illustrating the use of my improved instrument.
In these figures, like letters of reference indicate the same parts.
My instrument consists essentially of a sextant comprising, in the ordinary
manner, a small fixed mirror a and a large movable mirror b, but is characterized
by the means for controlling the motion of the latter.
The angular movement of the large mirror is effected, in my in-
strument, by means of a micrometer-screw c which engages with a toothed
sector fixed to this mirror b.
An opposing spring e constantly maintains the sector d in contact with the
screw c 50 as to prevent any lost motion.
The micrometer-screw bears a head f which enables it to be moved, and
which is divided into a hundred equal parts; this head moves opposite to a vernier
for enabling tenths to be read off.
The plate g which is fixed to the toothed sector d, and on which is mounted the
large mirror, bears an index or datum mark which moves opposite to
graduations marked on the table of the instrument, each division corresponding
to one turn of the screw e or of the head f.
The threads of the screw e and of the sector d are designed in such a manner
as to give the angle either in centigrades, i.e., hundredths of a grade (Centesimal
system), or in milliemes (thousandths of the distance).
When the measurement of the augle is to be evaluated in grades, each division
on the table of the instrument corresponds to 10 grades so that the vernier gives
centigrades.
P
When the measurement of the angle is to be evaluated in milliemes, each
division on the table of the instrument corresponds to a hundred milliomes and
the vernier gives the tenth of a millieme. (In the system of measuring angles
here referred to, 10 milliemies 1 centieme, and 160 centiemes 1 right angle.
The particular denominations of centieme and of millieme given to these new
measures are based on the fact that the arcs of the corresponding circle
are very approximately equal in length, to the th part and the oth part of
the radius of this circle, respectively. Thus, for a circle of radius 1000, the are
of the circle corresponding to a right angle has a length × 1000; on dividing
this length by 1600, one has the length of are corresponding to a millieme. which
length is approximately unity.
T
2
In order to enable the operator to find the desired distance without having to
make any calculation, the table i hears a slide rule comprising a divided rule j
made in two parts and a slider & operated by means of a pinion or screw engaging
with a rack on this slider k, and moving between the parts of the rule j.
The two parts of the said rule, as well as the slider, are provided with
graduated scales.
My instrument renders it possible to employ, for the purpose of measuring the
distance of any point, a method of operation which is quite new and presents
great advantages over all those heretofore employed, since it no longer requires
the operator to move either to the right or to the left, in order to lay out a base line.
This new method of procedure is as follows:-

page_text: Let A be the point where the operator is stationed, and M be the point of which
it is required to find the distance. The operator commences by taking a datum-
mark R; he then measures, by means of the instrument hereinbefore described,
the parallax or angle a which the two points M and 1 subtend at the point A:
the operator then moves forward up to the point B. towards the datum-mark,
through a distance which may vary, for example, between from about 25 to
50 metres, and he then mensures the parallax or angle which the points M
and R subtend at the point B.
Knowing the angles a and B, one can easily dednee the angle y which is equal to
The triangle RAM can then be solved, for one side, A B and the two angles ay
are known. If 7 be the distance A B, through which the operator advanced,
and the distanco (A M) sought, we have the relation : —
The graduated rule j mentioned above, has for its object to give the solution
of this equation directly; for this purpose, the rule proper bears two series of
logarithmic graduations or scales, oue B for distances, the divisions of which
correspond to different values of log. X and of which the graduations give the
value of the distance, the second C for parallaxes or angles, the divisions of which
correspond to the different values of log. sin B.
The slider itself bears a scale D) with logarithmic graduations, the scale of
differences, the divisions of which correspond to the different values of
log.
し
Bin (B-a).
This slider moreover bears a complementary scale E, the scale of baso lines,
permitting the operator to vary the length of the base line 7.
The scales shown in the drawing have been determined on the assumption
that the instrument evaluates the angular measurements in grades and conti-
grades.
To sum up, the measurement of the distance of any point is obtained in the
following manner, with my instrument :-
1. The operator chooses a datumn-mark either to the right or to the left of the
point considered;
2. He causes, by operating the micrometer-screw, the image of the point to
coincide with the datum-mark, or vice versa.
3. The operator walks in the direction of the datum-mark measuring a base-
line of from 25 to 50 metres.
4. He reads off, on the circular scale A, marked on the table of the instrument,
and on that on the head, the divisions before which the two datum-marks h,
traced, on the one hand, on the sector g, and on the other hand, on the reading
vernier of the head f respectively come to rest.
5. He again causes the two images of the two points considered, to coincide.
6. He reads off as before, the divisions before which the two dutum marks h, I
stop and obtains the difference of the two results.
7. He then moves the slider and brings the division or mark on the scale E,
corresponding to the base-line chosen, opposite to the same division of the
parallax or angle scale C as that of the scale A, before which there is the datum-
mark h.
8. He then reads off, on the scale of distances B, the division which is opposite

page_text: the division on the scale of differences D corresponding to the number found for
the difference of the two parallaxes or angles, and the division thus found on
the scale of distances B, gives the desired distance.
My improved instrument offers the great advantage of not requiring any fixed
support; morcover it takes up very little space and is capable of being carried
like a field-glass.
Thus for example, assume that, with a base of 50 metres, the last parallax or
angle found was 560 as indicated in Figure 1, and that the difference between
the two parallaxes or angles measured was 80, in divisions of the vernier; in
order to find the distance sought, I place the mark 50 on the Ecale E opposite
the division 560 of the scale C and I read off on the scale B, opposite to division 80
of the scale D, the distance 3200, which is the distance sought.
My improved instrument is moreover provided, on the underside of its table,
with a special arrangement for enabling angles of elevation to be measured.
This arrangement comprises a horizontal cross-wire collimator m, below which
is suspended a pendulum n the free end of which, provided with a vernier o,
moves opposite to a graduated scale F giving angles of elevation.
The divisions of this scale F' correspond, according to the method of con-
struction of the instrument, either to one grade or to 10 milliemes; the vernier o
of the pendulum giving tenths, thus enabling altitudes to be evaluated either
to 10 centigrades, or to one millieme.
In order to prevent the pendulum from continually oscillating, it is maintained
in its vertical position by means of any suitable spring device which the operator
releases when he wishes to take an observation.
In order to measure an angle of elevation, the operator directs the liue of
sight of the collimator m towards the point the height of which is sought; he
then bears on the small lever p so as to release the pendulum and the division
before which the said pendulum comics to rest, gives the altitude sought.
The sliding scales or slide rule jk, hereinabove mentioned, also permits the
altitude of the point considered relatively to the point of observation, to be
measured.
The operator first measures the angle of elevation, and obtains the distance of
the point as hereinabove described he then places the division of the scale of
differences 1) corresponding to the angle of elevation found, opposite to the
division on the scale of distances B corresponding to the distance found, and the
division of the scale of base-lines E which is opposite the division of the scale of
parallaxes or angles C corresponding to an angle of 90 degrees will give the
height sought.
Thus, for example, I assume that the point the altitude of which is desired,
is at a distance of 3200 metres and that the angle of elevation found is equal
to 80 centigrades, 1 bring the mark 80 of the scale D opposite the distance 3200
on the scale B and I read off, on the scale E, 26 metres opposite the division 1000
on the scale of parallaxes or angles C, which division corresponds to a right
angle.
My improved instrument, by reason of the combination of the sextant and the
pendulum-collimator, enables all altitudes to be evaluated, whatever be their
height; when the height is too great to be measured directly by the pendulum,
it is only necessary to take a datum-mark near the horizontal, the altitude of this
point is evaluated by means of the pendulum-collimator, then the parallax or
angle of this datum-mark is measured relatively to the point sought; the sum of
the two angles will give the angle of elevation of the point considered and,
consequently, the altitude of this point.
My improved instrument enables all the elements necessary for making a topo-
graphical survey to be measured and is, for this reason, capable of receiving
numerous applications.
It is obvious that I can modify the form, dimensions, and detail arrangements
of my improved instrument according to its various applications.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is :-
1. A topographical instrument for the measurement of angles, altitudes and
distances, consisting essentially of a sextant of which the angular displacements
of the large movable mirror are controlled by a micrometer screw bearing a
divided head moving opposite a vernier, the plate, on which this movable
mirror is mounted, bearing an index which moves opposite divisions marked
on the table of the instrument and each corresponding to one turn of the micro-
meter screw, substantially as described.
2. A topographical instrument for the measurement of angles, altitudes and
distances, consisting essentially of a sextant of which the angular displacements
of the large movable mirror are controlled by a micrometer screw bearing a
divided head moving opposite a vernier, the plato on which this movable
mirror is mounted bearing an index which moves opposite divisions marked
on the table of the instrument and each corresponding to one turn of the micro-
meter screw, the table of the instrument bearing a divided rule having two
branches between which moves a slide provided with a rack engaging with a
controlling pinion or screw, the two branches of the rule and the slide bearing
graduated scales enabling the distance of a point to be ovaluated by means of
the indications given by the sextant, substantially as described.
B
3. A topographical instrument for the measurement of angles, altitudes, and
distances, consisting essentially of a sextant of which the angular displacements
of the large movable mirror are controlled by a micrometer screw bearing
divided head moving opposite to a vernier, the plate on which this movable
mirror is mounted bearing an index which moves opposite divisions marked
on the tuble of the instrument and each corresponding to one turn of the micro-
meter scrow, the table of the instrument hearing a divided rule having two
branches between which moves a slide provided with a ruck engaging with a
controlling pinion or screw, the two brauches of the rule and the slide bearing
graduated scales enabling the distance of a point to be evaluated by means of
the indications given by the sextant, the instrument moreover comprising a
collimator beneath which is suspended a pendulum, the free ond of which bears
a vernier moving opposite a graduated scale giving the measure of angles of
elevation, substantially as described.
4. The improved topographical instrument constructed substantially as hereiu-
before described with reference to the drawing, for the purposes specified.
Dated on day or August 1900.
1. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agouts for the Applicant.