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Description of the Optigrapk . 
D; at the end of this frame is a plain mirror E, beneath 
which is suspended, by a universal joint, the telescope 
F, of which G is the eye-tube. H are sliding tubes, ca* 
pable of being shortened or lengthened in the same pro- 
portion as the inside speculum c, (fig. 4,) which is fixed 
to any place by the clamp screw P. The pencil L, 
of which h is the handle, slides perfectly easy, without 
shake, in the tubes H: the pencil is so contrived as 
to have all the freedom of a pen when held in the hand 
for use. 
Fig. 4, represents a section of the telescope, being the 
principal part of the invention. The rays from an ob- 
ject entering the plain mirror a, are reflected into the 
telescope, passing through the object-glass &, and en- 
tering the speculum c, are reflected through the eye-glass 
d , to the eye at e : f is a piece of parallel glass, with a 
small dot on its centre, exactly in the focus of the eye- 
glass d . 
Mode of Using the Qjptigraph . 
Fix the drawing board to the table (by a clamp which 
is packed in the box) so that the surface of the mirror E 
is nearly parallel to the object; then take hold of the han- 
dle h , and hold the pencil on that part of the paper where 
you would wish the centre of your drawing, or any part 
thereof, to be. Then place your eye at the eye-tube G, 
and with your left hand alter the inclination of the mirror 
E until the small dot, described at/, in fig. 4, is on some 
particular part of the object that you wish to begin with, 
adjusting the telescope to distinct vision by the milled 
head P. Then by moving your hand (having the pen- 
cil) you pass the dot seen in the field of the telescope 
over the object, the pencil marking it at the same time on 
the paper. 
