An Improved Apparatus for Drawing Elliptic Curves.
Year: 1895

page_text: Date of Application, 22nd June, 1895-Accepted, 26th Oct., 1895
COMPLETE SPECIFICATION.
[Communicated from abroad by V. EMANUELE CENTONZE, of Palace Sirignano,
Piazza Municipio, Naples, in the Kingdom of Italy, Artist.]
An Improved Apparatus for Drawing Elliptic Curves.
I, WILLIAM PHILLIPS THOMPSON, F.C.S. M.I.M.E. of The Agency for
Foreign Patent Solicitors, 31, High Holborn, in the County of Middlesex, 6, Lord
Street, Liverpool, and 6, Bank Street, Manchester, both in the County of Lancaster,
and Lower Temple Street, Birmingham, in the County of Warwick, Civil 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 :-
The elliptic compass which forms the subject of my invention is designed
essentially in correspondence with a well-known geometrical theorem that the
distance from any point on the curve to the two fixed points known as foci is constant
and equal to the major axis of the ellipse. The instrument is composed of a metallic
arc A. B. C. which rests by means of the part C upon the surface on which the
ellipse is to be drawn. The end A of the said arc bears a vertical shaft carrying
a point which serves to fix the centre of the ellipse. In a normal position to this
shaft is attached a metallic grooved piece indicated in the elevation Figure 1 of the
drawings by the letters D. E. and in the plan Figure 2 by the letters D¹D"
and E E" which piece bears at both ends two small pivots which form the foci of
the ellipse which is to be drawn. The distance between these two points can be
varied at will within certain limits by means of a screw K. M. double threaded in
opposite directions and which is easily turned by means of a thumb screw. This
arrangement enables one to draw ellipses of greater or lesser length. The two little
pivots are connected by means of a small metallic chain passing over a pulley O
placed upon a second arm P Q attached to the vertical shaft. This arm bears the
drawing point attached to it in the same manner as the pen or pencil of a compass
and the position of this drawing point is determined by a special screw actuated by
a thumb screw placed at the end Q. It is evident that by means of this apparatus
just as a drawing point placed upon the axle of the pulley O will draw an ellipse
which will have for its major axis the length of the little chain so a
point R fixed
upon the arm P. Q. will trace an approximate ellipse which has for its major axis
the length R. D. + R. E.
The following secondary modifications can be made in my instrument :-It may
be constructed either entirely of metal or if it be desired of larger dimensions partly of
wood or other material. The screw M. K. may be placed either above or below
the pivots which form the foci. The drawing point R which is connected to the
central axis by means of the arm P. Q. and which is adjustable at different distances
from the centre always kept in tension by means of a spring S and guided by means
of a little turntable carrying grooved rollers working on the edges of a slot in the
arm P. Q., and may also be caused to rotate by pressure of the hand and the spring
may be done away with. In place of the arc A. B. C. the compass might also be
fixed upon the drawing board by means of a support provided at its end with
three points. The dimensions of the elliptic curve which is to be traced depends
essentially upon the position of the pivots and the length of the chain and by varying
the length of the chain the compass may be caused to trace approximate ellipses
of various dimensions. The distance between the foci as is evident from the

page_text: drawing may be varied by means of the screw threaded in opposite directions but
the same may also be adjusted by any other equivalent mechanical system which
would serve to cause the two fixed points or foci to approach or recede from each
other.
my said
Having now particularly described and ascertained the nature of
invention, and in what manner the same is to be performed, I declare that what I
claim is :-
The compass for drawing. elliptic curvés consisting essentially of two pivots
which correspond to the foci of the ellipse and capable of being adjusted with
regard to each other by means of the right and left screw together with a chain
each end of which is attached to one of the two pivots and which determines the
outline of the elliptic curve and a vertical shaft which carries the drawing point
and being controlled by the chain by means of a pulley determines the major axis
of the ellipse substantially as above described and illustrated in the accompanying
drawing..
Dated this 01st day of Tune 1905
W. P. THOMPSON & Co.,
31, High Holborn, London, W.C., Agents.