a 
forced convergence,” that “it generally advances slowly to its 
new position,’ and he speaks of ‘the influence of time over 
the evanescence as well as the creation of this class of phe- 
nomena.” The nature of focal accommodation by action of 
the ciliary muscle was not then known—(1844). 
3. A. New Mops or STEREOSCOPY. 
cross-vision a large plane surface on which are regularly recur- 
"ing figures, such as wall paper, a phantom image of the wall is 
curved,’ but discusses this feature no further. His explana- 
tion” of the production of the phantom wall is easily under- 
stood. Let A, B, ©, ete. (fig. 3), be equidistant points on the 
wall, in front of which stands the observer whose eyes are at 
Rand If the right eye be directed to A and the left to A’, 
To make the curvature apparent, the optic angle must | 
arge; and on account of the exceeding muscular strain it In- 
