144 
wheels and pullies the friction will be very little and cause 
no perceptible impediment to the movements of the pencil 
in all directions. 
The DIORAGRAPH is thus used : 
Fix it in a horizontal position, with a proper bearing on 
the objects to be drawn ; which may be done by laying it on 
a table and fastening it with clamps, or by any other means, 
to prevent it from shifting. Have the drawing board pre^ 
pared with paper in the usual manner; drop it into its 
place, which should be so adjusted that the upper surface 
of the drawing board be a little lower than the upper sur¬ 
face of the frame ; then put on the T with its appendages, 
so that the wheels, on the cross part of it, be in the groove 
on the rail; adjust the sight and mark on the thread ; pre¬ 
pare a pencil, with the point so sharpened, that it be as near¬ 
ly as may be in the direction of its axis; slide it into the 
pencil case (which it should tightly fit) until the point pro¬ 
ject a little out of it; drop the pencil case, with the point 
of the pencil downwards, into its place on the port-pencil : 
then, looking through the sight hole, move the port-pencil 
so that the mark on the thread appears to move along the 
lines of the objects to be drawn, and the pencil will then 
mark on the drawing board a true perspective representa¬ 
tion of them. TheT, with its appendages, is then removed, 
the drawing board taken out, the irregularities of the pen¬ 
cil lines corrected, and the drawing finished in the usual 
manner. Thus may true perspective drawings of any ob¬ 
jects be made, with nearly as much facility as copies of pic¬ 
tures are taken, by laying paper on them and tracing on it 
the lines of the original, seen through it when held up to 
the light. 
At first some awkwardness will be experienced in moving 
the pencil, so that the ?nark shall follow the lines to be 
drawn ; but, after a little practice, it will be as easy as to 
follow the lines of a picture laid on a table before you, and 
can be done with equal expedition. 
