A NEW OR IMPROVED INSTRUMENT OR APPARATUS FOR DESCRIBING CIRCLES OR 'ARCS' THEREOF, AND FOR INDICATING ONE OR MORE OF THE RADIAL LINES."
Year: 1878

page_text: LETTERS PATENT to Thomas Parkinson Worthington, of Blackpool, in the
County of Lancaster, Architect, for the Invention of "A NEW OR IMPROVED
INSTRUMENT OR APPARATUS FOR DESCRIBING CIRCLES OR 'ARCS' THEREOF,
AND FOR INDICATING ONE OR MORE OF THE RADIAL LINES."
PROVISIONAL SPECIFICATION left by the said Thomas Parkinson Worthing-
ton at the Office of the Commissioners of Patents on the 17th April 1878.
THOMAS PARKINSON WORTHINGTON, of Blackpool, in the County of Lancaster,
Architect. 44
A NEW OR IMPROVED INSTRUMENT OR APPARATUS FOR DESCRIBING
CIRCLES OR ARCS' THEREOF; AND FOR INDICATING ONE OR MORE OF THE RADIAL
LINES."
This Invention relates to a new or improved instrument for describing, arcs of
circles of any required radius.
The apparatus consists of two wheels of different diameters mounted on a spindle,.
the distance apart being rendered adjustable by means of set screws or similar means..
This apparatus when set in motion freely on a level surface will travel in a regular.
curve on the same principle as a rolling cone.
In practice it is required to describe arcs of circles of considerable and definite.
radius, and if the ratio of the diameters of the wheels be known, it is easy by.
adjusting them to the proper distance apart on the spindle to describe such curves
with precision.
;
Example, the accompanying sketch will illustrate the principal features of my,
Invention. A and B are two wheels mounted on axis C and adjustable thereon by
set screws a.
The diameter of wheel A being represented by 30, and that of wheel B
by 29, and their distance apart by 24, the radius of the arc described by wheel A
when rolling freely on a plane surface will be 720.156 or thereabout.

page_text: By graduating the spindle C, any required are may be described by altering the
distance between the wheels.
The wheels may be made in any ratio, and the spindle graduated to correspond
therewith on the above principle. A handle D is provided for propelling the wheels
without interfering with their direction, and a pencil or marker E traces the course
of the wheel A upon the surface to be marked.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Parkinson Worthington in the Great Seal Patent Office
on the 16th October 1878.
THOMAS PARKINSON WORTHINGTON, of Blackpool, in the County of Lancaster,
Architect. "A NEW OR IMPROVED INSTRUMENT OR APPARATUS FOR DESCRIBING
CIRCLES OR ARCS' THEREOF, AND FOR INDICATING ONE OR MORE OF THE RADIAL
LINES."
This Invention relates to a new or improved instrument for describing or drawing
arcs of circles of any required radius, for indicating the radial lines and for measuring
the length of the portion of the circle so described.
The apparatus consists of two wheels of different diameters mounted on a
spindle or axis, upon which they slide freely, and are easily secured at any required
distance apart by set screws or other means. This apparatus when set in motion
freely on a true and flat surface will travel in a regular curve in the same manner
as a rolling cone, and by means of a pencil or by causing the larger wheel to act
as a marker, the delineation of the curve may be accomplished.
In practice it is required to describe arcs of considerable and definite radius in
offices, workshops, and places of limited area, when the centres from which the arc
is to be struck is far beyond the boundaries of such places.
By the use of my Invention such arcs may be readily described in such places
with accuracy and speed, as no centre is required to be found, it being only neces-
sary to know the semi-diameter or radius of the circle of which the arc is required,
and the wheels adjusted accordingly, as berein-after explained.
In order that my Invention may be more fully understood I have hereto annexed
a Sheet of Drawings illustrative thereof, wherein Fig. 1 is a side view of an instru-
ment for describing ares, constructed according to my Invention.
The apparatus consists of two wheels A and B of different diameters mounted on
a spindle or axis C, upon which they may be easily adjusted by means of set screws D
or other similar means.
The spindle C is graduated so as to form a scale by means of which the wheels
can be adjusted so as to describe the arc to the radius required. E is a handle for
propelling the instrument, to which handle is also attached a pencil holder F, through
which a pencil or marker may be passed.

page_text: The holder is secured by set screw G in the collar H, so that it can be readily
set to the edge of the larger wheel marked A. The wheel A by being marked on
the face, as shewn in Fig. 2, serves as a measure to indicate the length of the arc
described, and has also a diameter line as shewn, and by a similar diameter line on
the face of the wheel B when both are adjusted to same line or angle of axis, the
radial lines may be indicated at any portion of the arc by pointing off at each wheel
when the diameter lines come in contact with the drawing surface, and marking a
line through the two points, which line, if continued, will pass through the centre
of the circle.
If two such lines are drawn from different portions of the arc, they will neces-
sarily intersect each other at the centre:
Figs. 3, 4, and 5 illustrate a straight edge in combination with the are describing
apparatus by which the radial lines may still more readily be drawn.
J is the straight edge suspended from the axis by arms K at each end, the screws
L being provided so as to accomodate the straight edge to the drawing surface,
according to the variations of angles by having the wheels at various distances
apart.
The straight edges are adjustable and of various lengths to suit the distances
between the wheels.
Figs. 6 and 7 illustrate an improved construction of propelling handle and pencil
holder for use when describing circles or arcs. The pencil holder F is mounted upon
the axis in such manner as to be always parallel thereto whilst the propelling
handle E can turn upon the stud a.
The principle upon which the wheels are adjusted is explained by the following
formula. Let a represent size of larger wheel, and a-1 the size of smaller
wheel, and the distance between the wheels, then the radius of the arc or circle
struck or described by the large wheel will be a, b; it is easy therefore by adjusting
the wheels at the proper distance apart on the axis to describe any curve within the
limits of the instrument with precision.
As an illustration or example of the foregoing formula, it may be imagined that
the diameter of the larger wheel is represented by 100, and that of the smaller
wheel by 99, and the distance between them by 3, then according to the formula given
a = 100, a-1 = 99, b = 3, therefore the radius of the circle described will be a x b,
or 100 x 3 = 300.
The following table gives a few examples of graduations, according to their pro-
portional sizes of wheels. Column A gives the proportional size of wheels, and
column B gives the distance apart for each foot of radius.

page_text: being adjusted upon a graduated axis C, as and for the purpose herein shewn and
described.
Secondly. The employment in combination with the above of a marking instru-
ment and straight edge, as and for the purpose herein. shewn and described.
In witness whereof, I, the said Thomas Parkinson Worthington, have hereunto
set my hand' and' seal, this Tenth day of September, in the year of our
Lord One thousand eight hundred and seventy-eight.