An Improved Instrument for use in Preparing Perspective and other Drawings.
Year: 1899

page_text: Date of Application, 4th Feb., 1899-Accepted, 15th July, 1899
COMPLETE SPECIFICATION.
An Improved Instrument for use in Preparing Perspective and other
Drawings.
I, GEORGE MCMULLEN, of Perth, in the Colony of Western Australia, Architect,
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:
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This invention relates to improved means for use in preparing perspective and
geometrical drawings; its object being to provide an instrument whereby centro-
lineals may be produced with sufficient accuracy for the purposes of perspective
drawing and which may be readily adapted for use in drawing parallel lines.
Centrolineads are open to objection as they are not easily or conveniently adapted
for the purpose intended and are not capable of being readily adjusted for preparing
drawings in perspective on a large or small scale. These objections are obviated
in the improved apparatus hereinafter described. The instrument may be con-
structed of metal or other suitable material.
In the accompanying drawings, Fig. 1 is a plan of the instrument complete.
Fig. 2 is an elevation. Figs. 3 and 4 are transverse sections taken respectively on
the lines and y-y, Fig. 1. Fig. 5 is a transverse section taken on the
line z-z, Fig. 1.
The blade A has its outer or working edge bevelled or chamfered and is con-
nected to the blade B by means of slotted links C and D whereof the extremities
work on pivots cd, c¹ d¹.
The pivots c and d are carried by tongued slides a, which work in slots,
adapted for their reception, formed in the blades A and B. The respective
pivots c and d are fixtures in the blades A and B. The links C and D besides
being arranged to pivot at their extremities are also furnished with an adjustable
pivot E, carried by the tongued slide F, the latter working in the grooved slot
in the link D. The pivot E passes through another tongued slide F¹ which is
capable of being moved along the grooved slot in the link C by means of the
screw G; the latter being furnished with a milled turning nut G₁. The tongued
slide F passes freely along the screw H and may be secured in position thereon
by the nuts H H¹.
For determining the radius of any circle desired and the angle of any perspective
required, the link C is marked with the respective distances of the centre of the
circle from a point in the centre of the blade A. When the pivot E is brought
opposite this figured distance and the blade B held stationary, converging or
approximately converging lines may be produced along the blade A. Thus,
perspective or convergent lines may be drawn with approximate accuracy, such
lines apparently converging to a long and inaccessible vanishing point. As an
illustration: If the link is set at 9 feet and the pivot is fixed there, the lines
which are drawn along the blade A will converge, approximately, to the centre of
a circle having a radius of 9 feet and so with any other measurements to which the
nivat may be fixed

page_text: When the pivot E is fixed in the centre of the link C as shown, the lines drawn
along the blade A will be parallel. The improved centrolinead can thus be readily
adjusted to serve as a parallel rule, such rule being capable of doing the work
straightforwardly instead of in the manner achieved by parallel rules of the usual
construction. This will be found a great advantage. The instrument may also
be used for doing the work of an ordinary T-square.
I is a fixing piece whereby the instrument may be secured to a drawing board
or other surface; the blade B being hinged to the said fixing piece at K. I¹¹ are
screws for adjusting the angle of inclination of the blade B. All the pivots are
provided with nuts.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I claim:―
1. The improved instrument for use in preparing perspective drawings and for
drawing parallel lines, constructed or operating substantially as described with
reference to the accompanying drawings.
2. An instrument for use in preparing perspective drawings and for drawing
parallel lines constructed substantially as herein described and comprising a
pair of slotted blades connected by slotted links, the latter being pivoted together
and to the blades.
3. In an instrument for use in preparing perspective drawings and for drawing
parallel lines, the herein described means for effecting the adjustment of the
pivot E, same comprising a scale on the link C, a tongued slide F¹ and a screw G
for operating the tongued slide F¹.
4. In an instrument for use in preparing perspective drawings and for drawing
parallel lines, the combination, with the blades A, B, of the slotted links C, D, the
pivots c, c, d, d, the tongued slides a, b, the adjustable pivot E, the tongued
slides F, F, and the screws G, H, substantially as and for the purpose set forth.
5. In an instrument for use in preparing perspective drawings and for drawing
parallel lines, the combination, with the blades A, B, connected by the links C, D,
of the fixing piece I and set-screws I¹, I¹, substantially as and for the purpose
set forth.
"