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(Camera Lucida . 
Since the size of the whole instrument, from being so 
near the eye, does not require to be large, I have on many 
accounts preferred the smallest size that could be exe- 
cuted with correctness, and have had it constructed on 
such a scale, that the lenses are only three quarters of 
an inch in diameter. 
Though the original design, and principal use of this 
instrument is to facilitate the delineation of objects in 
true perspective, yet this is by no means the sole purpose 
to which it is adapted ; for the same arrangement of re- 
flectors may be employed with equal advantage for copy- 
ing what has been already drawn, and may thus assist a 
learner in acquiring at least a correct outline of any sub- 
ject. 
For this purpose the drawing to be copied should 
be placed as nearly as may be at the same distance be- 
fore the instrument that the paper is beneath the eye- 
hole, for in that case the size will be the same, and no 
lens will be necessary either to the object, or to the 
pencil. 
By a proper use of the same instrument, every purpose 
of the pentagraph may also be answered, as a painting 
may be reduced in any proportion required, by placing 
it at a distance in due proportion greater than that of 
the paper from the instrument. In this ease a lens be- 
comes requisite for enabling the eye to see at two unequal 
distances with equal distinctness, and in order that 
one lens may suit for all these purposes, there is an 
advantage in carrying the height of the stand accord- 
ing to the proportion in which the reduction is to be ef- 
fected. 
The principles on which the height of the stem is ad- 
justed will be readily understood by those who are ac- 
customed to optical considerations. For as in taking a 
perspective view the rays from the paper are rendered 
