Reflecting Telemeter for Vessels.
Year: 1896

page_text: Reflecting Telemeter for Vessels.
I, AURELIO BELLENI, Naval Sub-Lieutenant, of the Italian Navy, residing at
13 Corso Umberto, Taranto, Italy, do hereby declare the nature of this invention
to be as follows:-
This invention relates to improvements in reflecting telemeters for vessels.
Some of these improvements could be applied to ordinary sextants for obtaining a
delicate adjustment of the reflecting mirrors as the greatest exactitude is necessary
in measuring small angles. While however the instrument constructed according
to this invention in general lines resembles a sextant, it is principally intended for
application as a telemeter, because with the special arrangements hereinafter
described, it enables distances to be measured by means of the reflection of the ship
in the two mirrors.
This telemeter is shown in front elevation and in plan in Figs. 1 and 2 of the
accompanying drawings.
R, R', R", is the frame supported on three feet, P, P₁, P. The foot P" also
serves as a guard to the axis of the large mirror S'analogous to that of the sextant.
S is the small mirror, silvered on one half but not silvered on the other, analogous
to that of the sextant; this small mirror S is retained in a frame corresponding to
that of Troughton & Simms' sextant, such frame being fixed to the free arm m' of
the large spring M₁ by two screws m³, as shown in the drawings. By means of
two parallel screws m having large heads, the position of such free arm m¹ of the
spring M' can be adjusted, the curved end of such spring forming the centre of
this movement. The other arm m² of the spring M' is fixed to the plane of the
instrument. Such spring M¹ is used instead of the connection which in Troughton
& Simms' sextant is interposed between the frame of the small mirror S and the
plane of the instrument, and it enables the sinall mirror to have delicate azimuthal
movements for effecting the correction of the mirrors, that is, for rendering such
small mirror parallel to the larger one without having to move the alidade of the
latter, as it is necessary to do in ordinary sextants. D, D' is an axis which carries
the screw V as well as an upright truncated cone of steel t. and the drum K, K¹, K",
around the cylindrical surface of which is arranged a silver ribbon on which the
graduation is engraved. The drum as well as the truncated cone t, may be made
in one with the axis D, D!. bz is a small rod having its extremities of agate;
this rod is fitted and can slide in the direction of its axis, within the tube T, T¹.
A B is the alidade of the large mirror; at the point B of this alidade the end b of
the small rod bears with simple friction, the distance from A to B being
80-4 millimetres; the spring M holds the said rod in contact with the point B.
The support L bears the fiducial line. The ring I is similar to the ordinary
G is a wooden
support of a telescope of a sextant, but it is not screw-threaded.
handle, ma spring serving to regulate the movement of the screw V the pitch of
which is 6 millimetres and which cannot have a travel longer than two pitches.
This screw works in a nut pierced in the hub Q supported by the three meeting
arms N, N', N"
Operation. By causing the drum K, K¹, K", to turn, the screw V advances and
the small rod bz is always forced by the spring M against the surface of the

page_text: Cue andane aut
It will be understood that if the pitch of the cone is changed, the angle through
which the large mirror will pass will also change in consequence, so that if this
difference is increased this angle will proportionately increase. With the object of
changing the size of this angle, exchange truncated cones are provided which may
be used one instead of the other so as to have the large mirror pass through several
angles of different sizes.
For graduating the instrument, first of all the mirrors are arranged parallel
(in their initial position as shown in the drawings) and zero is marked on the silver
ribbon at the point which corresponds with the fiducial line; then the drum is
caused to turn until the zero point comes back for the second time to the fiducial
line. During this time the large mirror will have travelled through an angle of a
certain number of degrees and minutes; this number naturally is multiplied by two,
for, as in a sextant, the angle formed by the mirrors is the half of the angle of the
objects; and one will thus have in degrees and minutes the greatest angle
measurable by the instrument. The helix described by the centre of the fiducial
line along the silver strip during two turns of the drum is divided in this number of
degrees and minutes, taking into account that the angular way of the dram K, K',K",
is proportionate to the angle described by the large mirror S'. The distance in
millimetres between two successive divisions of one ininute can be readily ascertained
according to the following formula, where a represents this unknown distance;
Double the length of
the circumference of
the drum in milli-
metres
:
the greatest angle
measured by the in-
strument in exactly : 11
two turns of the
drum
The instrument as so far described is a simple angle measurer. For taking a
distance with the instrument, the angle of depression of the ship at the horizon
should be measured, the number of degrees and minutes being read immediately on
the graduated silver strip on the drum K, K', K", and afterwards from this angle
and from the elevation of the observer's eye on the sea the distance coull be
ascertained by reference to a table, (such for instance as that of Carnet de l'Officier
de Marine, on page 56, entitled "Table pour l'Appreciation des Distances en Mer").
In order however to avoid the loss of time necessitated by reference to a table,
instead of writing degrees and minutes on the silver strip, the corresponding
distances as given in the table are marked thereon.
As the angle of depression for the same distance will vary according to the
elevation of the observer on the sea, the instrument must be provided with as many
drums carrying graduated silver strips as there are stations of varying elevation.
on the sea in which the instrument will be used, and for this reason the drum
is arranged as shown in the drawing so that it can be changed with great
facility.
To ascertain the distance of a vessel from the observer, supposing the latter is at
an elevation of 30 metres on the sea, all that it will be necessary for him to do will
he to measure the angle of depression of the vessel at the horizon after having
inserted the drum graduated for the elevation of 30 metres, when he will at once
be able to read the distance without any further calculation.
With regard to the vertex angle of the truncated cone t, such angle will vary
according to the elevation at which the instrument is to be used. For instance, if
it is desired that the instrument shall be able to measure a greatest angle of 3° 15'
(approximately corresponding to the distance of 500 metres for the elevation of
30 metres on the sea) it will be sufficient for the large mirror S¹ to be able to turn
through an angle of so that the small rod b z can advance such a distance
3º 15'
2
as to cause A B to turn throngh an angle of 1° 37' 30", and to find such distance it

page_text: will be sufficient to make in regard to the smaller side a right angled triangle
having the other side A bequal to 80-4 millimetres, and the angle opposite to the
unknown side equal to 1° 37' 30". This distance will thus be found to be
2.28 millimetres. But the degree of sliding of which the small rod bz is capable
is produced by the pitch of the cone during two turns of the axis D D¹ which
carries it, and during two turns of the drum K, K, K", and during these two
turns the truncated cone is moved downwards a distance equal to double the pitch
of the screw V, such distance being 12 millimetres. Therefore it will be sufficient
to so construct the truncated cone that the difference between the radius of its top
and that of its bottom shall be equal to 2.28 millimetres, and its height 12 milli-
metres, from which particulars it will be easy to find the vertex angle of such
truncated cone, which will be 21° 31' 8", in accordance with which the truncated
cone would be made.
If it is desired that the instrument shall be capable of measuring a different
greatest angle, the same method of calculation is adopted and a different truncated
cone employed which can easily be substituted for the other as shown in the
drawing.
It will of course be necessary in using a second truncated cone to make new
graduations on the silver strip by twisting round the drum as previously
described.
Dated this 15th do 1000
ALLISON BROS.,
Agents for the Applicant.
I. AURELIO BELLENI, Naval Sub-Lieutenant, of the Italian Navy, residing at
13 Corso Umberto, Taranto, Italy, 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 improvements in reflecting telemeters for vessels..
Some of these improvements could be applied to ordinary sextants for obtaining a
delicate adjustment of the reflecting mirrors as the greatest exactitude is necessary
in measuring small angles. While however the instrument constructed according
to this invention in general lines resembles a sextant, it is principally intended for
application as a telemeter, because with the special arrangements hereinafter described,
it enables distances to be measured by means of the reflection of the ship in the
two mirrors.
This telemeter is shown in front elevation and in plan in Figs. 1 and 2 of the
drawings filed with the Provisional Specification.
R, R', R", is the frame supported on three feet P, P, P". The foot P₁ also
serves as a guard to the axis of the large mirror S¹ analogous to that of the sextant.
S is the small mirror, silvered on one half but not silvered on the other, analogous
to that of the sextant; this small mirror S is retained in a frame corresponding to
that of Troughton & Simms' sextant, such frame being fixed to the free arm m¹ of
the large spring M¹ by two screws m³, as shown in the drawings. By means of
two parallel screws m having large heads, the position of such free arm m¹ of the
spring M can be adjusted, the curved end of such spring forming the centre of this
movement. The other arm m³ of the spring M₁ is fixed to the plane of the
instrument. Such spring M' is used instead of the connection which in
Troughton & Simms' sextant is interposed between the frame of the small
mirior S and the plane of the instrument, and it enables the small mirror to have.

page_text: delicate azimuthal movements for effecting the correction of the mirrors, that is,.
for rendering such small mirror parallel to the larger one without having to move
the alidade of the latter, as it is necessary to do in ordinary sextants. D, D¹ is an
axis which carries the screw V as well as an upright truncated cone of steel t, and
the drum K, K', K", around the cylindrical surface of which is arranged a silver
ribbon on which the graduation is engraved. The drum as well as the truncated
cone t, may be made in one with the axis D, D'. bz is a small rod having its
extremities of agate; this rod is fitted and can slide in the direction of its
axis, within the tube T, T¹. A B is the alidade of the large mirror; at the
point B of this alidade the end 6 of the small rod bz bears with simple friction,
the distance from A to B being 804 millimetres; the spring M holds the said rod
in contact with the point B. The support L bears the fiducial line. The ring I is
similar to the ordinary support of a telescope of a sextant, but it is not screw-
threaded. G is a wooden handle, m a spring serving to regulate the movement of
the screw V the pitch of which is 6 millimetres and which cannot have a travel longer
than two pitches. This screw works in a nut pierced in the hub Q supported by the
three meeting arms N, N', N".
Operation. By causing the drum K, K', K", to turn, the screw V advances
and the small rod bz is always forced by the spring M against the surface of the
truncated cone, and in its movement it carries the alidade and the large mirror.
It will be understood that if the pitch of the cone is changed, the angle through
which the large mirror will pass will also change in consequence, so that if this
difference is increased this angle will proportionately increase. With the object of
changing the size of this angle, exchange truncated cones are provided which may be
used one instead of the other so as to have the large mirror pass through several
angles of different sizes.
For graduating the instrument, first of all the mirrors are arranged parallel (in
their initial position as shown in the drawings) and zero is marked on the silver
ribbon at the point which corresponds with the fiducial line; then the drum is
caused to turn until the zero point comes back for the second time to the fiducial
line. During this time the large mirror will have travelled through an angle of a
certain number of degrees and minutes; this number naturally is multiplied
by two, for, as in a sextant, the angle formed by the mirrors is the half of the augle
of the objects; and one will thus have in degrees and minutes the greatest angle
measurable by the instrument. The helix described by the centre of the fiducial
line along the silver strip during two turns of the drum is divided in this number
of degrees and minutes, taking into account that the angular way of the
drum K, K', K", is proportionate to the angle described by the large mirror S'.
The distance in millimetres between two successive divisions of one minute can be
readily ascertained according to the following formula, where represent this
unknown distance;
Double the length of
the greatest angle
the circumference of
the drum in milli-
:
metres
measured by the in-
strument in exactly
two turns of the
drum
::
:
11
The instrument as so far described is a simple angle measurer.
distance with the instrument the angle
For taking a
of the hin

page_text: As the angle of depression for the same distance will vary according to
the elevation of the observer on the sea, the instrument must be provided with as
many drums carrying graduated silver strips as there are stations of varying
elevation on the sea in which the instrument will be used, and for this reason
the drum is arranged as shown in the drawing so that it can be changed with great
facility.
To ascertain the distance of a vessel from the observer, supposing the latter
is at an elevation of 30 metres on the sea, all that it will be necessary for
him to do will be to measure the angle of depression of the vessel at the
horizon after having inserted the drum graduated for the elevation of 30 metres,
when he will at once be able to read the distance without any further
calculation.
With regard to the vertex angle of the truncated cone t, such angle will vary
according to the elevation at which the instrument is to be used. For instance, if
it is desire that the instrument shall be able to measure a greatest angle of 3° 15'
(approximately corresponding to the distance of 500 metres for the elevation
of 30 metres on the sea) it will be sufficient for the large mirror S' to be able to
3° 15'
turn through an angle of , so that the small rod b can advance such a
2
distance as to cause A B to turn through an angle of 1° 37' 30", and to find such
distance it will be sufficient to make in regard to the smaller side a right angled
triangle having the other side A equal to 80.4 millimetres, and the angle opposite
to the unknown side equal to 1° 37' 20". This distance will thus be found to
be 2.28 millimetres. But the degree of sliding of which the small rod b = is capable
is produced by the pitch of the cone during two turns of the axis D D' which
carries it, and during two turns of the drum K, K, K", and during these two turns
the truncated cone is moved downwards a distance equal to double the pitch of the
screw V, such distance being 12 millimetres. Therefore it will be sufficient to so
construct the truncated cone that the difference between the radius of its top and
that of its bottom shall be equal to 2.28 millimetres, and its height 12 millimetres,
from which particulars it will be easy to find the vertex angle of such truncated
cone, which will be 21° 31' 8", in accordance with which the truncated cone would
be made.
If it is desired that the instrument shall be capable of measuring a different
greatest angle, the same method of calculation is adopted and a different truncated
cone employed which can easily be substituted for the other as shown in the
drawing.
It will of course be necessary in using a second truncated cone to make
new graduations on the silver strip by twisting round the drum as previously
described.
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 1
claim is :-
The improved telemeter constructed substantially as described and as shown in
the drawings.
ALLISON BROS.,
Agents for the Applicant.