IMPROVEMENTS IN APPARATUS OR INSTRU- MENTS FOR DESCRIBING OR DRAWING ELLIPTICAL FIGURES
Year: 1864

page_text: PROVISIONAL SPECIFICATION left by Henri Reda de St. Martin at the
Office of the Commissioners of Patents, with his Petition, on the
18th June 1864.
I, HENRI REDA DE ST. MARTIN, of No. 53, Willes Road, Prince of Wales
Road, Kentish Town, in the County of Middlesex, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN APPARATUS OR INSTRU-
MENTS FOR DESCRIBING OR DRAWING ELLIPTICAL FIGURES," to be as follows:-
My Invention consists in describing or drawing with greater accuracy.and
facility than has hitherto been effected, any outlines having an elliptical form;
in drawing smaller figures of this description than any instrument or method
at present in use has been capable of producing, at least in a manner suffi-
eiently feasible and practical to be universally adopted.
The apparatus which I propose to construct for the aforesaid purpose is a.
compass composed of three legs, two of which are to be not only articulated
at the point of junction, as in the ordinary mathematical compass, but are to be
so connected with the third leg by means of a ring or collar that they may be
enabled to revolve round. it with facility. One of these two legs is to be fur-..
nished at its, lower extremity with a pen or pencil, the other leg being princi
pally used as a guide bar. As an example method of construction, I propose
in the third leg, which when in use is always to be maintained stationary and
in a perpendicular position, to make a slot or groove throughout, a great part:

page_text: of its length. This slot is made for the reception of the axis or axle of a
half ring or semicircular plate, the diameter or size of which should bear a
certain proportion to the magnitude of the whole instrument in question. The
said half ring, besides moving up and down the stationary leg of the compass
as far as the slot will permit it, is made to turn on the axis before mentioned,
so that it may be adjusted by means of a screw to any inclination or angle
desired. It will be perceived that if the half ring be placed in a horizontal
position at any elevation on the stationary leg of the compass, and the rotary
leg furnished with a pen be brought in contact with its outer edge and made
to pass round it, the figure delineated by the pen at the end of the leg will
be a semicircle; but that if the half ring be inclined and the rotating leg be
guided round its exterior, that then the figure described will be a semi-ellipse
more or less pronounced according to the obliquity or inclination of the half
ring.
I propose to complete the ellipse in the following manner :-The two
revolving legs aforesaid are to be connected with each other by means of a
bar, one end of which is fixed to either of the legs though articulated at
its junction therewith; whilst the other end is made to slide up and down the
second leg by means of a ring or otherwise.
It is obvious that this connecting bar will enforce an invariable similarity
in the position and movements of the two rotating legs relatively to the
stationary leg, and it will also be perceived that these legs being on opposite
sides of the one which is stationary, the three legs being always maintained
in a straight or direct line, when the describing leg, or that which is fur-
nished with a pen, has achieved the semi-ellipse, and arrived at the extremity
of the half ring, the second or guide leg will have just attained the opposite
extremity of the said half ring; now, if the guide leg be made to pass along
the edge of the half ring, the pen leg will describe the other half of the ellipse
and thus complete the figure desired. As the size of the semi-ellipse will
increase or diminish according to the position, high or low, which the half
ring occupies in the slot, the stride of the movable legs being increased as the
said half ring rises in the slot, it will be necessary in some way to increase the
length of the pen leg so that it may reach the surface on which the ellipse is
to be described. As one method of effecting this I make the leg tubular
instead of solid, and insert therein the shank of the pen or pencil with which
the ellipse is to be drawn. By this means it will be seen that the shank of
the pen will have a telescopic movement, and serve the purpose of a length-
ening bar.
I propose also to enlarge or diminish the size of the ellipse without shifting

page_text: the position of the half ring on the stationary leg, by fixing a bar horizontally
to the end of the pen leg and connecting a pen or pencil with it in such a
manner that the said pen may slide upon the bar and be adjusted to any dia-
meter which it may be desired to give the ellipse.