* 
ea & 
- and stone and reproduced by the thousand. 
4 % > 3 : 
). IN. Rood on producing Stereographs by Hand. 
As in using this table objects in the extreme foreground are | 
supposed to be 25 inches distant from Q, we have for them not 
a displacement 1-900 in. but 0: for the 26th inch, viz. the Ist _ 
inch of depth in the picture the quantity ‘022, &. Thus if we 
know the distance from the spectators of the objects to be repre- 
sented, they can be located on the stereograph. In the same 
manner tables are constructed which apply to objects placed at 
greater distances from the eye. Indeed after some practice very 
tolerabie stereoscopic representations of many objects can 
made without reference to such tables. (See drawing.) 
This process was originally devised by me for the production — 
of stereoscopic representations of optical phenomena, which when — 
well executed form almost a substitute for the real illustrations. — 
Photography for obvious reasons is not well adapted to this — 
class of object 
many of these effects are greatly enhanced. The phenomena of 
complementary colors, and many other facts of 3h | 
not. i 
the same gentleman has suggested to me, be rendered intelligi — 
ble by the stereoscope without the use of costly apparatus. The 
stereoscope is thus capable, in the hands of an expert teacher, — 
of a far wider range of use than was at first seen. E 
At the suggestion of Dr. W. Gibbs, I have also made a few 
stereoscopic drawings of erystal models: these can be drawn 
by this instrument with perhaps greater facility and rapidity than _ 
ts. , 
. 
any other ¢lass of objec th 
The accompanying stereoscopic diagram was drawn with my 
a fees pip eco ve tab é : 
utline sketches of eve escription stereoscopi wings - 
of ideal objects or of obec not fat x ion ae: craps 
man, are by this process readily executed—problems evidently — 
beyond the power of photography. 
Finally the drawings thus made can be transferred to wood 
Troy, Oct, 11th, 1860. 
