[ 37] 
N° IL 
Explanation of an Optical Deception. 
BY D. RITTENHOUSE. 
sere 29) OME experiments were long ago commu-- 
ss nicated to the Royal Society of London, 
fhewing, that through the double microfcope, the furfaces 
of bodies fometimes appear to be reverfed, that is, thofe 
parts which are elevated feem depreffed, and the contrary. 
But the caufe of this appearance, for any thing I know, 
remains ftill to be explained. 
In order to produce this effe&, no other apparatus is 
neceflary than two convex lenfes placed in a tube, at a 
diftance from each other nearly equal to the fum of their: 
focal diftances.. Through thefe glaffes, objets that appear 
diftin@lly, always appear inverted; for they are not feen 
direQly, but by means of an image formed either between 
the two glaffes, or between both of them and the eye. 
If we look through fuch glaffes at cornifhes, picture: 
frames and other mouldings in carpenters work, and fome 
forts of carved work, thofe parts which are raifed general~ 
ly appear deprefled, and thofe parts which are deprefled 
appear raifed. But a very ready obje@t, and which fuc- 
ceeds as well as any thing I know of, is a-brick pave-- 
ment; whether it be a chimney-hearth, or pavement out 
ot doors. Viewed through the tube above defcribed, every” 
little cavity in the bricks, and the chinks between them, 
almoft always appear to be fo many elevations above the 
furface of the bricks. 
When I confidered this odd appearance, the firft pro-. 
bable caufe that offered was, that thofe parts of the object 
which are funk, and fartheft from the eye, might have 
their correfpondent parts of the image formed by the glai- 
fes neareft to the eye, and therefore would appear raifed. 
But: 
