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LAVII. Description and Use of an Instrument called “ The 
Sectograph,” principally intended for the Purposes of di- 
viding right Lines into equal Parts, measuring Angles, 
and inscribing Polygons in the Circle, fc. Sc. invented 
by Tuomas Jones, Astronomical and Mathematical In- 
strument Maker, &c. No. 21, Oxendon-Street, 
Severat years have now elapsed since J first thought of 
the arrangement for this instrament; but though I obtained 
a patent for it about two years ago, I have tll now been 
prevented from submitting it to the public by various pro- 
fessional duties which I could not lay aside ; being obliged, 
like every man who tries to attain excellence in his pro- 
fession, to finish the greater and most particular parts of 
my instruments with my own hands. 
The sectograph will, I hope, effect the purposes intended; 
namely, a considerable saving of time, and a degree of ac- 
curacy applicable to the various purposes of drawing. The 
instrument is very simple in its construction, and easy in 
its use ; requiring only oue setting or adjustment for divid- 
ing, laying down, or measuring any space or angle; and 
with a facility calculated to lessen the laborious part of 
these processes, and to render them light and pleasant to 
the careful and elegant draughtsman. — 
The common size of the sectograph is about eight inches 
long, and measures to the extent of that distance. The 
instrument is packed in a morocco case (with a printed de- 
scription inside) the exterior of which is about nine inches 
Jong, and three quarters of an inch square*, 
Description of the Instrument. 
The bars of metal (or other substance) (P].VI.) A,H,B, are 
of equal dimensions, the bars a, a, a, a, a, are likewise equal 
to each other. The whole of the eight bars are of the same 
length, and are pinned and screwed together at the dots and 
small circles, where the ends of the smaller bars join the 
larger ; each joint giving an easy and pleasant motion. 1, 3, 
5,and7 are small short pieces placed across, and pinned 
to the others. 0, 1, 2, 3, 4,5, 6, 7 and 8 are the places 
where the steel points are fixed into the bars. e,g, is a scale 
with a slit in the middle, which receives the clamp and 
fixing screw x, for holding the points at any required di- 
* The price of the eight-inch is two guineas, that of others in proportion 
to their lengths, &c. as they are made to any size, with any number 9 
points, or without the clamp and scale, if required. 
f 
Vol. 42, No. 198. Dec. 1813, Ce stance, 
