A NEW (OR IMPROVED) POCKET INSTRUMENT FOR LEVELLING AND FOR MEASURING VERTICAL ANGLES
Year: 1876

page_text: LETTERS PATENT to Carl Bohne, of Berlin, in the Kingdom of Prussia, for the
Invention of "A NEW (OR IMPROVED) POCKET INSTRUMENT FOR LEVELLING AND
FOR MEASURING VERTICAL ANGLES,"
Sealed the 11th July 1876, and dated the 14th January 1876.
PROVISIONAL SPECIFICATION left by the said Carl Bohne at the Office of
the Commissioners of Patents on the 14th January 1876.
CARL BOHNE, of Berlin, in the Kingdom of Prussia. "A NEW (OR IMPROVED)
POCKET INSTRUMENT FOR LEVELLING AND FOR MEASURING VERTICAL ANGLES."
In surveying for the construction of railways I have felt the want of an
instrument which having a compendious form might be suitable to mark with
sufficient exactitude and without long manipulations the horizontal direction and
vertical angles of the ground. I propose to supply this want by the adoption of
the instrument herein-after described and forming the subject of this Invention.
My improved instrument needs no staff head, and is of so ininute a form that it
may be conveniently carried in the pocket. It indicates almost immediately not
only the horizontal direction like the telescope level, but also gives measurements
for the tangents of the vertical angles lying within sight. These qualities and its
low price (about twenty shillings) will I believe lead to the use of this instrument
for surveys or levellings not requiring the greatest accuracy, which can only be
obtained by the telescope level. This instrument is also suitable for surveying the
strata lines for topographical plans, provisory levellings, and cross profils for
projected railways and causeways, also for drainings and other agricultural works,
for paviors, and other mechanics, and it may be used instead of the plumb level in
building.
The accompanying Sheet of Drawing shows an instrument embodying my
Invention.
"6
A, A', indicating a cardanic" suspension or gimbals, the "cardan" rings being
of red brass and moving on cylindrical steel axles with a certain sensibility.
B, B', a pendant stirrup or frame fixed on the interior ring by the two small
screws band 6 of which the line of conjunction forms angles of 45 degrees with the
axles of the "cardanic" suspension.
C, C, a small tube fixed in the frame B, B₁, and containing the measuring
parts, namely,
c, a biconvex lens as eye glass screwed on to a separate small sliding tube with
[Price 10d.]

page_text: an opening of nearly 1. centimeter, the left and right edge of which is smoothed
so far as to leave to the remaining central stripe a breadth of only 4–5
millimeters, thus allowing a clear sight between it and the setting to the right
and left.
.
cl, a glass micrometer, 1 centimeter in diameter, placed within the focal dis-
tance and nearly in the focal point of the lens in such a manner that its dividing
lines in a distance of 1 millimeter shall be horizontal in consequence of the free
suspending position of the frame B, B', and of which the middle line is marked
expressly for the horizontal axis of sight by extending as diameter over the
whole plate, whilst the lines of the other full millemeter have 3, those of the 1
half 2, and of the others millemeter in length; instead of the micrometer
a diaphragm witli a simple line or hair sight may be used for the purpose of
levelling only.
.D, DI, a metal disk fixed at the lower end of the stirrup or frame, the weight
of which assists in keeping the stirrup or frame perpendicular, and the edge ]
and bottom of which are covered with an elastic coating.
-
d, d¹, a little screw on this disk parallel to the line of sight to rectify it.
E, E, a cylindrical casing which by means of a screwed cover bears the screwed
external ring of the "cardanic" suspension, and which surrounds the above
mentioned moving parts in such a manner that their free movement is not hindered
if this casing is held almost perpendicularly by the handle E", and a contact of the
inner side and these moving parts is only possible by means of the clastice edge
coating of the disc D, D'.
e, ell, two disks of selected plate glass placed in a parallel manner diametrically
opposite to each other in the side of the casing, which in conjunction with the free
suspending position of those parts allows a free look through the tube C, C¹, without
causing a disturbing diversion of the rays of light.
F, F, a screw passing lengthwise through the handle E, and which when
screwed up presses against the elastic bottom of the disk D, D¹, stopping the use of
the inner mechanism; by merely turning back the screw the mechanism is free to
work again..
The surrounding case, its screw cap, and the stopping screw must close.
hermetically, so that the outer currents of air, dust, and atmospheric moisture are
prevented from passing into the inner compartment.
In the employment of the instrument I assume the invariableness of the rectified
and self-directing plane of sight, that is to say, of the lines optical of sight through
the centre of the ocular lens, and through the upper or under edge of the middle
line of the micrometer. This rectification will be effected as with the levelling
telescope or by means of a similar instrument, displacing the centre of gravity of the
moveable parts by the adjusting screw d, d. For this purpose the cover or cap with
the above mentioned suspending parts is unscrewed, and after a first correction it is
compensated by the constant diversion of the rays of light passing the glass disks of
the cage.
The rectified instrument placed nearly perpendicularly to the eye after turning
back the stopping screw will settle the horizontal direction of the visual axe, and
the more precisely the greater the sensitiveness given to the "cardanic" suspension.
However, for the use in free hand the sensibility must not surpass a certain
degree.
The precise direction of the line of sight depends at the same time upon the
diameter of the " cardanic" rings and of the lower position of the centre of
oscillations of the moveable parts, the instrument shown being only 155 grammes in
weight, 105 millemeters in total length, and 37 millemeters in diameter may
approach the smallest form. This diameter is however also sufficient to employ a
combined lens instead of a simple one for the diminution of spheric aberration. But
to make the division of the micrometer more striking than would be possible by the
lens alone the glass plate is covered before the division with a very fine stratum of
varnish, and the division is corroded by means of hydrofluoric acid gas, in order

page_text: that it may be blackened in a durable manner with a coloring substance rubbed
with oil.
It would be possible to provide the instrument with a telescopic arrangement,
but this would prejudice more or less its compact and convenient form, low price,
and simplicity of construction,
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by the
said Carl Bohne in the Great Seal Patent Office on the 12th July 1876.
CARL BOINE, of Berlin, in the Kingdom of Prussia. "A NEW (OR IMPROVED)
POCKET INSTRUMENT FOR LEVELLING AND FOR MEASURING VERTICAL ANGLES."
In surveying for the construction of railways I have felt the want of an instru-
ment, which while being of a compendious form and easily handled, could be used
to mark with accuracy the horizontal direction and vertical angles of the ground
to be surveyed. To supply this want I have constructeil the instrument herein-
after described which needing no staff head and being minute can be carried about
by the surveyor in his pocket without any inconvenience. It not only indicates
like the telescope level the horizontal direction, but further, the tangents of the
vertical angles in view may also be measured at the same time.
These qualities
and the low price of about 30 shillings are sufficient recommendations to bring
the instrument in question into general use.
In addition to the purposes already enumerated it can also be used for measuring
distances and heights, and for surveying purposes in general, where absolute
accuracy is not requisite for surveying the horizontal strata lines, in topographical
plans, for provisonal levellings, and cross profils or off-sets for railway projects, for
highways, for drainings, and other agricultural improvements, for paving, and more
especially as a substitute for the plumb level in building.
Terrestrial objects can either be viewed through a small telescope of only 28mm in
length, of peculiar construction, having a microscopic sight of five-fold magnifying
power at most, which fulfils in double manner the purpose of a "Galileo" telescope
with diaphragm or with a more simple instrument; the visual lines may be seen
through a convex lens, the lateral segments of which are cut, the terrestrial objects
beside and behind the lens being at the saine visible to the naked eye.
The accompanying two Sheets of Drawing show an instrument embodying my
Invention.
A, A', indicates a "cardanic" suspension or gimbals, the rings being of red brass,
and moving on cylindrical steel axles with the requisite sensibility.
B, B', a pendant bow stirrup or frame fixed symmetrically to the inner sides of
these rings by means of the small screws b, b₁, so that the line of conjunction stands
at an angle of 45° to the axles of the "cardanic" suspension.
C, C', a small tube fixed in and supported by the frame B, B', and containing
the measure indicating parts that either as at Sheet I. represents a " Galileo "
telescope.
Firstly. From double to 24 fold magnifying power:
:-
c a plain or a biconvex object glass of, say either 58 or 39mm focal distance, with
an opening of 16mm.
e a plain or a biconvex lens of, say from 25 to 20mm focal distance with an
opening of 10mm as part of the eye glass.
3, a biconcave diverging lens of the same crown glass applied with and before
the latter, and which has a fine perforation in the middle and the hinder surface of
which, of say from 12 to 10mm radius of curvature, joins the convex lens, whilst
the front surface of either 12 or 7.3mm radius, and with an opening of 8 to 9mm
conducts the rays of light falling through the object glass achromatically and
regularly diverging to the eye.
cl, a glass micrometer within the focal distance and near the focus of the convex

page_text: lens, and on the plane side of the object glass 15mm in diameter, the dividing lines.
of which of a millimeter apart from one another, and cut by a perpendicular,
are in consequence of the suspended position of the bow or frame B, B₁, horizontal,
and the middle line of which is marked expressly for the horizontal axis of sight,
and extends as diameter over the whole surface of the plate, whilst the lines of b
the other full millimeter are 3 those of the balf millimeter 2, and those of the
remaining millimeter 1mm in length, otherwise and for the sole purpose of
levelling there may be substituted in lieu of the micrometer a diaphragm with a
simple line or hair sight.
Or, Secondly. Of 4 and similarly of 5-fold magnifying power:-
c, an object glass of 36mm focal distance and 14mm openings.
ci, a plain convex magnifying glass of either 25 or 121/ mm focal distance, and 10mm
opening, and in the centre of which there is cut for the eye lens of telescope a
spherical concave of 8.7mm focal distance or a concave with a radius of 4.35mm
and an opening of 4mm.
c", a glass micrometer in above described division, or if with a focal distance of
the convex lens of 10mm a millimetre is divided into 20 parts, or a simple
diaphragm may be substituted.
D, D, a metal disk fixed to the lower end of the bow or frame B, B¹, the weight
.of which more exactly regulates the perpendicular position of the latter, and the
edge and bottom of which are furnished with an elastic lining.
d, d', a small screw on this disk parallel to the line of sight and for rectifying
the same.
E, E, a cylindrical receptacle with screw cover or cap, into which the outer ring
of the "cardanic" suspension is screwed, and which surrounds the parts just men-
tioned in such a manner as not to hinder their free motion if the instrument is
suspended perpendicularly before the eye, and held by the handle E", contact of these
moveable parts with the receptacle can only take place against the elastic lining of
the disk D, D¹.
e, el, two disks of selected plate glass fixed diametrically opposite to each other in-
the side of the receptacle, and which when the above-mentioned parts are in a-
freely suspended position, permits an unimpeded look or clear sight through the tube
C, C, without causing a disturbing deviation of the rays of light.
F, F, a screw passing lengthwise through the handle Eu, and which when
screwed up presses against the elastic bottom of the disk D, D', and puts the inner
apparatus out of use by keeping it against the surrounding case; by merely turning
back this screw the apparatus is free to work again.
The surrounding case, its screw cap, and the stopping screws, must close hermeti-
cally in order to prevent currents of air, dust, and atmospheric moisture from getting
to the inner compartment.
In describing the employment of my improved instrument I assume the invari-
bility of the rectified and self-directing horizontal plane of sight, that is to say, of
the lines of sight through the so-called optical centre of the ocular lens or eye
glass, and through the upper or under edge of the middle line of the micrometer.
This rectification is performed in the same way as with the common levelling
telescope or similar instrument, by displacing the centre of gravity of the moveable
parts by means of the adjusting screw d, d'; for this purpose the cover or cap with
its suspending parts is unscrewed, and after a first correction the constant deviation
of the rays of light passing through the glass disks of the case or receptacle must
be compensated for. If the rectified instrument after the turning back of the
stopping screw be placed nearly in a perpendicular position, it will itself settle the
horizontal direction of the visual axis, with more or less exactness according
to the degre of sensitiveness given to the "cardanic" suspension. Nevertheless
when the instrument is used in the free hand this sensitiveness must not exceed a
certain limit. If the rings move on steel prisms or cones in bearings of the same
metal, with the least possible friction, then the beating of the pulse of the hand
causes oscillations of the inner mechanism, and the horizontal line is only to be
]

page_text: perceived in the periodically returning interferences, and such a construction would
only be practicable if the instrument when used be firmly supported. But if the
rings composed, say of red brass, move by means of cylindrical well polished steel
axles, then the slight friction is sufficient to paralyse, the instrument being held in
the hand the mechanical effect of the beating of the pulse, or the involuntary
motions of the hand in general, so that instead of the oscillations there arise only
slight momentary and synchronical pulsations of the inner mechanism through
these movements, between which the visual lines steady and define themselves
clearly, and through which these lines return all the more precisely to the same
position as soon as the instrument is intentionally inclined sideways in any
direction. These pulsations likewise prove that when in use the inuer mechanism
does not rest against the case, and with my improved instruments, as abovo
described, this can only take place when the deviation from the perpendicular
position exceeds 10°. Moreover the influence of the involuntary movements of the
hand can be moderated or increased as may be necessary, by leaning the instru-
ment when looking through it against the eye hole, or by shaking it gently in a
cross direction towards the other cyc.
The precise acquisition of the horizontal line depends of course on the greater
diameter of the "cardanic" rings, and on the lower position of the centre of
oscillations of the moveable parts the telescopic instrument shown in Sheet I., which
weighs 190 grammes, with a total length of 116 centimeters, and a diameter of
43 centimetres; and the other simpler instrument, in Shect II., which weighs.
155 grammes with a length of 106 centimetres, and a diameter of 37 centimetres
may be considered of the smallest practical size. However the diameter of the
latter is sufficient to employ a combined lens instead of a simple one for the
diminution of the spheric aberration.
Further, to make the division of the micrometer more striking than is possible by
the lens or by putting a dazzling tube before the objective side, and even to make
it appear quite black, the glass plate before the division is covered with a very fine
stratum of varnish, then the division is corroded by means of hydrofluoric acid gas,
and a blackening substance is rubbed in with oil, or for obtaining greater fineness
it is cut with a diamond suitable for the purpose, but then the instrument turned
towards the eye must be protected against the light falling in sideways, so that the
rays penetrating from the back suffer a total reflection on the slanting and smooth
cut surfaces. If then the instrument be held for immediate use before the eye the
latter will see unimpeded by the glass disks of the receptacle by means of part of
the pupil and of the concave ocular lens, the upright virtual picture of the terrestrial
objects lying before, and by means of the other part of the pupil and of the uncovered
middle, and also of one part of the ring-shaped convex lens, the middle division line
passing through as horizon, and the aggrandized remaining micrometer division
thrown on that virtual picture at the same time the telescope presents such sharply
defined pictures, even of objects scarcely 4 decrimetres distant, that there is no
need of regulating the glasses, or of a compensation of the centre of gravity.
In a similar way, with the simpler instrument, the eye will see by means of
part of the pupil and of the perpendicular lens stripe the micrometer division and
also the line or hair sight enlarged, but by means of the other part of the pupil and
of one or both of the open segments beside the lens, the terrestrial objects directly,
and covered by those enlarged division lines. In the same way will the telescopic
instrument distinctly mark the perpendicular micrometer line on the optical
pictures of even quite near objects, and in a similar way the simpler instrument,
for which the perpendicular is cut more sharply, will in due course perform the
same, so that both of them can be used in building for adjusting without being
disturbed in stormy weather, as is the case with the plummet.
The eye is so much accommodated during these operations as to be but little
fatigued, and the glasses of the telescopic instrument for a middling position are
fixed for a terrestrial distance of from 10 to 20 metres, whilst if they are fixed at

page_text: Whilst in case of need the pictures of still nearer objects can exactly be observed
by means of a weak convex lens allowing the micrometer still to be visible.
Moreover, the visual line to a micrometer point represents the principal ray to
the 1st principal point of the lens, and the parallel with this ray from the 2nd
principal point to the eye, and thereby for the simple instrument with a thickness
of the bi-convex lens of 4mm and 10mm joint radius of the curvatures the distance
between the micrometer and the eye lens amounts to 8/.
Finally, experience shows that in pre-calculated telescopic systems, notwith-
standing the short focal distance of the object glass, the dispersion without
employment of flint glass is sufficiently annulled, and that the refracted rays
in the object glass are united by the both aplanatic and achromatic operating cyo
lens, presenting almost similar angles of refraction, but turned in opposite direction
to new picture points and suitable to achromatic pictures, on which, by means of
the operation of the convex parts of the eye lens, the micrometer division is
clearly represented, and in which even with combined eye lens the scarcely 1mm
great perforation of the concave glass disappears. But as the micrometer with a
horizontal axis of sight forms a vertical plane the remaining division lines
thrown on the optical pictures, and also directly on to the terrestrial objects,
indicate the tangents of the angles of elevation and depression, the numerical
co-ordination of which agreeing exactly with the magnifying to be calculated can
be reckoned and set in tables for use with another instrument for measuring angles
or by the crossing of the upper and lower edges of the uniform thick divisional
lines on a levelling staff placed vertically at a certain distance for an angular
accuracy of from 6 to 15 minutes. This instrument may be used in the same
manner to measure the tangents of oblique and horizontal angles when the right
angled divisional lines of the micrometer is pointed towards the angle plane, and
the axis of sight in the one side of the angle and the crossing of the other in the
micrometer is measured, it may also in some cases be used in combination to reduce
oblique angles to the horizon. Furthermore, the millimeter of the division cut
off in the telescopic instrument, with the magnifying co-efficient m and the distance
W between the micrometer and the first principal of the convex eye lens on a
levelling staff standing vertically at 100 meter distance meters, or,-
10
m w

page_text: .
1.,
ULIC
20mm micrometer distance;
or if
°
=
1°/ m 5, W=10mm the half millimeters,
and if
2° m=4, and also 5, and W25, and also 20mm the whole millimeters
of the micrometer cut off on the levelling staff placed at 100 meters distant 1 meter,
and thus the instrument is to be used; for instance, by taking off cross profils in a
hundred-fold proportion of the measures cut off from 1/2 or from 1 millimeter in
the different distances at the same time for measuring distances.
Further, it will indicate the elevation and depression of a terrestrial point which
is at a distance D found either on the chart or by more or less careful measurement.
cut by the nth micrometer-line above or below the horizontal direct
约 D
-
=5.100
and also n. meters above or below the horizontal.
. D
1000
1
In the same way the instrument. without telescope will calculate with its 1
micrometer at 10mm from the lens, according to the 10 or 100-fold proportion of the
measures cut off from 1 or 15 millimeter the distances and the elevation or
depression of an object in the horizontal distance D cut by the nth micrometer
part; for instance, the height of a tree at a supposed length=
'D
= 100
Further, in the combinations and 1 and 1ª the visual lines through the 1st, 2nd, 2
3rd
millimeter tenth
above or below the horizontal represent the rational tangent lengths 0.2; 0·4;
0:0
of the appertaining angles of elevation and depression for a
or in other words direct the rational rise and fall proportions of the ground 2 pro
radius 100;
=
1
I p.m.; 2 p.m.; 3 p.m.
Also the instrument without telescope with micrometer 10mm distant from the
eye glass, the visual lines diverging under 34 minutes through the
1st, 2nd, 3rd
25th millimeter tenth
above or under the horizontal represent the tangent lengths
1; 2; 3;
"
25
of the appertaining vertical angles for a radius
and the rise and fall proportions
10 p.m.; 20 p.m.; 30 p.m.
250
p.m.
= 100
after which the eye can still interpolate middling degrees, and also it is possible for
it to survey still steeper degrees by means of the latter instrument to 400 p.m., or
an angle of elevation and depression up to 221, by looking more slantingly through
the lens. Other optical systems would, especially if the cataptric arrangements are
made use of, allow of obtaining a greater magnifying power, but only at the expense
of the field of view and of the simplicity, and therefore the above described con-
structions will prove more practical.
At the same time the instrument in question will allow in actual levelling the
reading of the cut-off' measures in distances up to 60 or 200 meters with an accuracy
varying but a centimeter if it is held before the eye whilst the body stands steady
in one position, or if it is supported by a light staff fixed on the ground and if at
the same time a levelling staff is used on which the whole and half decimeters in
due breadth are marked alternately in black and white colours, the half and whole
meters being also distinctly marked for the perspective.
Finally, the instrument can-when in use be carried by a string attached to the
handle, and when in transport enclosed in a box with cover, the handle upwards.
In the bottom of the box is cut a round hole for reception of the handle which

page_text: can then be used as a support, placing it in an inverted position on something
solid.
The instrument with telescope and with combined ocular gives the greatest
clearness of pictures but not the greatest field of sight.
The micrometer division may also be produced by means of photography, and for
this purpose can be transferred to collodion covering the plane surface of the glass,
the blackening fineness and proportion being regulated according to requirement.
Having now described and ascertained the nature of iny said Invention, and in
what manner the same is or may be performed, I desire it to be understood that I
do not confine myself to the particular shape of apparatus shown on the annexed
Drawings, nor to any precise dimensions, or to the use of any particular metal or
material, as such may be varied to suit the circumstances of particular cases; and
that I claim as secured to me by the herein before in part recited Letters Patent,-
Firstly. The entire combination of my improved pocket levelling instrument,
whereby it can be used for the purposes already stated with the simplest operations
and without being disturbed by external influences, substantially as herein-before
described.
Secondly. The manner of securing the moveable apparatus by means of a
"cardanic" suspension, so that when the instrument is held in the open hand the
incchanical influence of the strokes of the pulse are neutralized by a comparatively
small friction of the axles of the "cardanic" rings, whereby instead of oscillations
only slight and momentary pulsations of the inner apparatus arise, which may
moreover be easily diminished if desired, and by means of which in co-operation
with the centre of gravity the visual axle can be obtained more exactly automatic
and almost absolutely horizontal, substantially as herein-before described.
Thirdly. In the telescopic instrument :-
1°. The peculiar construction of the "Galileo" telescope, whereby I produce with-
out the employment of flint glass, but by means of nearly equal angles of refraction
in opposite direction as experience may direct, clear and achromatic dioptric pictures,
even of quite near objects, say, only a few decimeters distant, and for the distinct
inspection of which an adjusting of the glasses of the hermetically enclosed inner
apparatus is not necessary.
2°. The peculiar construction of the concave ocular whereby it is adapted at the
same time for the observation of the pupil, and with the other part the mi-
crometer, by being a ― combined for ordinary use and for smaller, let us say,
two-fold magnifying power of a plano-convex and of a sharper bi-concave lens,
the latter of which has in its centre a small perforation for the exposure of the
summit of the concave lens; and further by containing - for exceptional cases,
especially for proportionately stronger, for example, four-fold magnifying power,
the concave cut immediately in the summit of the convex lens, which construction
and magnifying power causes indeed more difficulties for obtaining clear pictures
and for incising of the micrometer lines, the whole substantially as herein-before
set forth.
Fourthly. The peculiar construction of the micrometrical dioptra in the instru-
ment without telescope in which the side segments of the micrometer eye glass are
filed or cut off, and the eye perceives with one part of the pupil through the open
segments beside the lens the terrestrial objects direct, but with the other part of
the pupil and through these lines of the lens the magnified micrometer division on
these objects, substantially as herein-before described.
In witness whereof, I, the said Carl Bohne, have hereunto set my hand and
seal, this Sixth day of July, in the year of our Lord One thousand eight
hundred and seventy-six
CARL BOHNE. (L.S.)