Instrument for Ascertaining the Radius or the Centre of a Circle to which the Sides of an Angle are Tangential.
Year: 1898

page_text: Instrument for Ascertaining the Radius or the Centre of a Circle
to which the Sides of an Angle are Tangential.
I, GUSTAV RUDOLF GEISER, of 128, Dufourstrasse, Zürich, Switzerland, Electrical
Engineer, do hereby the nature of this invention to be as follows:
This instrument has for its object to ascertain readily in a graphical manner the
radius or centre of a circle to which two points in the sides of an angle are
tangential. It is formed of horn, celluloid or other suitable transparent sheet
material, and may be of rectangular shape having however a sector piece of an
acute angle with radial sides cut out of it but not quite to the centre which latter is
marked by or provided with a needle hole. A number of equidistant circles are
marked on the instrument. Along each side may be provided a graduated by
preference metrical scale with up and down numeral indications.
To use the instrument for finding the radius it is placed upon the angle in
question, said angle having a point marked off on each side or leg equidistant from
the apex.
One of these points say in the right hand leg is made to fall in the line
of one side say the left of the sector cut and the instrument is then shifted about
until the points marked on the legs of the angle are tangential with one of the
circles. A radius line can then be drawn along the left side of the sector cut and
the instrument is then turned round its centre to the left, a needle or the like being
passed through its centre hole until the same left side of the sector cut intersects
the point on the other leg of the angle, whereupon another radius line can be
drawn along the same left side of the sector cut. Where the two radius lines
intersect is the centre to be ascertained. After some practice the centre can be
found even if the legs of the angle do not fall on one of the circles but somewhere
between two such. The size of the radius can be read off upon one of the graduated
scales. The graduations at the top of the instrument may be united by cross lines,
thus forming a parallel scale with say ten or twenty metrical cross division lines.
To find the centre, when the radius is given, the instrument is by preference
modified in form, that is to say the sector cut need not be made, and the concentric
circles need not be carried more than about half round for the smallest, and the
others less and less of a circle, otherwise the instrument would become uselessly
wide or large, especially for railway designing work where the outer circles would
have large radius.

page_text: to which the Sides of an Angle are Tangential.
I, GUSTAV RUDOLF GEISER, late of 128, Dufourstrasse, Zürich, but now of Stans,
Unterwalden, both in Switzerland, Electrical 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 instrument has for its object to ascertain readily in a graphical manner the
radius or centre of a circle and is formed of horn, celluloid or other suitable
transparent sheet material.
Fig. 1 shews the instrument in a rectangular form for the purpose of readily
finding the radius or centre of a described circle or of the circle to be described to
which the sides of a given angle are tangential, the tangent points being also
given. A sector piece of an acute angle with radial sides is cut out of it but not
quite to the centre which latter is marked by or provided with a needle hole. A
number of equidistant circles are marked on the instrument. Along each side
may be provided, as here shewn, a graduated, by preference metrical, scale with
up and down numeral indications.
To use the instrument for finding the radius it is placed upon the angle in
question. Let Fig. 2 represent say an obtuse angle and let the points a and b equi-
distant from the apex be the tangent points to the circle, the centre of which is to be
found. Then place the instrument on the angle as shewn in Fig. 3 so that one of the
points, for instance b, is made to fall in the line of one side, in this case the left,
of the sector cut out. The instrument is then shifted about until the points a
and b on the legs of the angle are tangent points to one of the circles marked on
the instrument. A radius line c Fig. 4 can then be drawn along the left side
of the sector cut, and the instrument then turned round its centre to the left,
a needle or the like being passed through its centre hole, until the same left side c
of the sector cut intersects the point a on the other leg of the angle, whereupon
another radius line d Fig. 4 can be drawn along the same left side of the
sector cut. Where the two radius lines intersect is the centre to be ascertained.
After some practice the centre can be found even if the legs of the angle do not
fall on one of the circles marked on the instrument but somewhere between two
such. The size of the radius can be read off upon one of the graduated scales.
The graduations at the top of the instrument may as shewn in Fig. 1 be united by
cross lines thus forming a parallel scale with say ten or twenty metrical cross (livision
lines.
When the instrument is to be employed simply to find the centre of a circle to be
described of a given radius or it may be to find the radius or centre of a described
circle it is by preference modified to the form shewn in Fig. 5. A sector cut is not
needed in this case, nor need the circles be carried more than about half round for
the smallest and the others will be less and less of a circle. Otherwise the instru-
ment would become uselessly wide or large especially for railway designing work
where the outer circles would have large radii.

page_text: Having now particularly described and ascertained the nature of my san
invention, and in what manner the same is to be performed, I declare that what
I claim is:
£ instruments as and for the purposes set forth.
Having now particularly described and ascertained the nature of my san
invention, and in what manner the same is to be performed, I declare that wha
I claim is:
instruments as and for the purposes set forth.
Dated this 27th day of December 1898.
Dated this 27th day of December 1898.
JENSEN & SON,
77. Chancery Lane, London, W.C., Patent Agents.