Improved Tangent Sight with Spirit Level Index for Cannon.
Year: 1898

page_text: Improved Tangent Sight with Spirit Level Index for Cannon.
I, HEINRICH KORRODI, Captain of Artillery, of 6, Rue des Archives, Berne,
Switzerland, do hereby declare the nature of this invention to be as follows:-
In tangent sights, with spirit-level indexes, hitherto introduced, in which the
graduated rod or scale is bent according to an arc of a circle having the sight pin
for centre, the centre of rotation of the spirit level index is arranged on the
graduated rod or tangent scale in such a manner that the graduation or marking
which indicates the angle of earth is eccentric in relation to the graduation giving
the tangent sight. As the graduation for the angle of earth must be in the
vicinity of that giving the tangent sight, it results from this eccentric arrange-
ment of the two graduations that the diameter of the spirit-level index is always
very small in relation to that of the graduated are indicating the sight, and that
for the purpose of reading off or point adjustment of an angle of earth, with a
certain degree of exactness, it is necessary to have recourse to verniers, which makes
the handling of the spirit-level index complicated.
The new sight, which forms the object of this invention, obviates the incon-
venience mentioned and allows of the exact reading or adjustment to point of
an angle of earth by means of a single graduated are, the diameter of which is per-
ceptible equal to that of the graduated are giving the sight; this result is obtained
by means of a spirit-level, moveable along the tangent scale, that is to say, the
centre of rotation of which coincides with the centre of the curve of the tangent
scale, that is with the sight pin, hence the graduation indicating the angle of earth
may be given on the tangent scale itself side by side with the graduation indicating
the sight.
In one way of carrying out this invention a sight-slide operated by a screw
is arranged to slide in the head of the tangent scale. The tangent scale is curved
according to an arc of a circle having the sight pin for centre and the guide for
the tangent scale has a sweep according to an arc of a circle, likewise having the
sight-pin for centre. On the side of the tangent scale a mortise groove is formed
as an arc of a circle concentric to the scale in which a spirit-level is arranged
to slide. On the back face and along the back rim of the lateral face of the
tangent scale, is the graduation or marking, indicating the sight; along the front
rim of the tangent scale is the graduation indicating the angle of earth. The
pointing of the spirit-level, for a given angle of earth, is effected by the moving of
this level along the tangent scale, without taking into consideration the momentary
position of the scale, the fixing of the spirit level in the desired position is effected
by means of a set-screw. The tangent scale is furnished on its back face with
teeth and gears with a pinion, which is provided with a fly wheel worked by
hand, by means of which the tangent scale may be adjusted to point.
The pinion can be put out of engagement with the teeth on the scale when it is
desired to shift the scale directly by hand before the exact adjustment to point.
In the improved sight, the graduated are indicating the angle of earth having

page_text: a diameter sufficient for this graduation being entirely visible and, consequently,
it being quite easy for anyone to read or exactly point an angle of earth, it is
clear that indirect pointing may be more frequently employed than in the past,
since the inconvenience of indirect pointing, resulting from the difficulty of exact
point adjustment of the spirit level is henceforward obviated.
The advantages of indirect firing which consist among others in a considerable
reduction of the field of dispersion of a battery, and in the possibility of firing at
an object concealed by the smoke or otherwise, may in the future be better taken
advantage of, since the rapidity and accuracy of the fire will no longer be
injuriously affected by the difficulty of an exact point adjustment, resulting from
the deficiency of the existing spirit level indexes.
Compared with tangent sights with spirit level indexes, hitherto employed,
in which the spirit level, the graduated circle and the point adjusting arrangement
are in the head of the graduated scale, the present sight has the further advantage
of a better disposition of the weight on the scale and enables the pointer to observe
the spirit-level without being obliged to leave the pointing position, the spirit
level being at the side of the scale in place of on the head thereof.
Tated this 28th dor of October 18OS
WHEATLEY & MACKENZIE,
40, Chancery Lane, London, W.C., Agents.
improved Tangent Sight with Spirit Level index for Cannon.
I, HEINRICH KORRODI, Captain of Artillery, of 6, Rue des Archives, Berne,
Switzerland, 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:-
In tangent sights, with spirit level indexes hitherto introduced, in which the
graduated rod or scale is bent according to an arc of a circle having the sight pin
for centre, the centre of rotation of the spirit level index is arranged on the
graduated rod or tangent scale in such a manner that the graduation or marking
which indicates the angle of earth is eccentric in relation to the graduation giving
the tangent sight. As the graduation for the angle of earth must be in the
vicinity of that giving the tangent sight, it results from this eccentric arrange-
ment of the two graduations that the diameter of the spirit-level index is always
very small in relation to that of the graduated are indicating the sight, and that
for the purpose of reading off or point adjustment of an angle of earth, with a
certain degree of exactness, it is necessary to have recourse to verniers, which makes
the handling of the spirit-level index complicated.
The new sight, which forms the object of this invention, obviates the incon-
venience mentioned and allows of the exact reading or adjustment to point of
an angle of earth by means of a single graduated are the diameter of which is per-
ceptibly equal to that of the graduated arc giving the sight; this result is obtained
by means of a spirit-level, movable along the tangent scale, that is to say, the
centre of rotation of which coincides with the centre of the curve of the tangent
scale, that is with the sight pin, hence the graduation indicating the angle of earth
may be given on the tangent scale itself side by side with the graduation indicating
the sight.
In the accompanying sheet of illustrative drawings, Fig. 1 is a side view,
Fig. 2 a. back view and Fig. 3 a sectional plan of tangent sight apparatus con-

page_text: structed according to this invention. Fig. 4 is a diagrammatic view showing the
application of the tangent sight.
On
In the head a of the tangent scale, a sight slide 6 operated by a screw is
allowed to slide. The tangent scale c is curved according to an arc of a circle
having the sight pin for centre and the guide for the tangent scale has a sweep
according to an arc of a circle, likewise having the sight-pin for centre.
the side of the tangent scale e a mortise groove is formed as an arc of a circle
concentric to the scale, in which a spirit-level e is arranged to slide. On the back
face and along the back rim of the lateral face f of the tangent scale, is the
graduation or marking indicating the sight; along the front rin of the tangent
scale is the graduation indicating the angle of earth. The pointing of the spirit
level for a given angle of earth is effected by the moving of this level along the
tangent scale, without taking into consideration the momentary position of the
scale. The fixing of the spirit level in the desired position is effected by means of
a set-screw. The tangent scale is furnished on its back face with teeth and gears
with a pinion which is provided with a wheel worked by hand, by means of which
the tangent scale may be adjusted to point. The pinion can be put out of engage-
ment with the teeth on the scale when it is desired to shift the scale directly by
hand before the exact adjustment to point.
The manner of employing the new tangent sight will be easily understood upon
reference to Fig. 4 of the accompanying drawing.
On the right hand side of this figure is a representation of ground, on which
is the mark Z aimed at. The line A B C represents the axis of the bore of the
cannon; A B Z is the trajectory of the projectile; VOZ the line of sight and
HOH the horizontal line passing through the sight pin.
DIRECT POINTING AT THE ELEVATED MARK Z:
Let n be the sight corresponding to the estimated distance of the mark Z, and
indicated on the tangent scale for example in thousandths of the curve radius of
such scale. The tangent scale is adjusted so that its division n corresponds with
the point zero of the sight graduation of the guide d and the cannon is then
pointed directly at the mark Z by means of the sight groove and the sight pin.
As will be seen in Fig. 4, the inclination of the axis of the cannon consists of
the sight or elevation n and the angle of earth 2 (likewise indicated on the
tangent scale in thousandths of its curve radius). The angle p may be determined
in the following manner: The spirit level e° remaining at the zero point of the
graduation or marking indicating the angle of earth is parallel with the line of
sight VOZ and forms an angle p with the horizontal line HO H. In order to
bring it to the horizontal position it is necessary to cause it to rise from the arc p
into the sheave hole or mortise of the tangent scale, that is to say the graduation
or marking division for which it will be in the horizontal position will precisely
indicate the angle of earth sought for. The piece having served for pointing at
the mark Z can thus indicate the angle of earth to the other pieces of the battery
which could be adjusted for firing without direct pointing, simply by means of the
sight and the spirit level in an uniform manner which would considerably limit the
dispersion of the range of the battery.
INDIRECT POINTING :,
For this purpose it is necessary previously to know the angle of earth. If the
mark is visible, this angle can be determined by one of the pieces of the battery
as indicated above; if the mark is not visible the angle of earth will be determined
by the map or in any other manner. Let n be the sight corresponding to the
distance of the mark and p the angle of earth. The tangent scale will be adjusted
as before, so that the division n of its graduation corresponds to the zero point
of the slide and the spirit level will be put at the lowest point on the division p of
the tangent rod. In operating the elevating screw of the cannon the cannon will be
caused to form an angle n+p with the horizontal, which will take place when
the spirit level is again in the horizontal position. If the angle of earth is negative,

page_text: that is to say, if the object is below the position of the cannon, the procedure will
be the same, care being taken however to adjust the spirit level on the lower'
graduation of the tangent rod.
In the improved sight, the graduated are indicating the angle of earth having
a diameter sufficient for this graduation being entirely visible and consequently,
it being quite easy for any one to read or exactly point an angle of earth, it is
clear that indirect pointing may be more frequently employed than in the past,)
since the inconvenience of indirect pointing, resulting from the difficulty of exact
point adjustment of the spirit level is henceforward obviated.
The advantages of indirect firing which consist amongst others in a considerable
reduction of the field of dispersion of a battery, and in the possibility of firing at
an object concealed by the smoke or otherwise, may in the future be better taken
advantage of, since the rapidity and accuracy of the fire will no longer be'
injuriously affected by the difficulty of an exact point adjustment, resulting from
the deficiency of the existing spirit-level indexes.
Compared with tangent sights with spirit-level indexes, hitherto employed,
in which the spirit level, the graduated circle and the point adjusting arrangement
are in the head of the scale, the present sight has the further advantage
of a better disposition of the weight on the scale and enables the pointer to observe
the spirit-level without being obliged to leave the pointing position, the spirit
level being at the side of the scale in place of on the head thereof.
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. The improved tangent sight with spirit-level index for cannons, in which
the exact reading and point adjustment of an angle of earth by means of a single
graduated are of a diameter perceptibly equal to that of the graduated arc indicating
the sight are rendered practicable by a spirit-level movable along the tangent
scale, that is to say, having its centre of rotation coincident with the centre of the
curve of the scale, that is with the sight pin in such a manner that the graduation
indicating the angle of earth may be given on the scale itself, at the side of the
graduation indicating the sight.
2. The improved tangent sight with spirit-level index for cannons substantially
as described with reference to the drawings.
Dated this 8th day of March 1899.
WHEATLEY & MACKENZIE,
40, Chancery Lane, London, W.C., Agents.