Trans. N. Y. Ac. Sez. "~ 120 Feb. 20, 
angle formed by the planes of the cards on which the pictures have 
been have made. 
Mr. STEVENS proceeded to explain and illustrate these effects in a 
series of diagrams, showing how this curious and novel result is due 
to the fact that, through the crystalline lenses, the images of the sim- 
ilar drawings, obliquely viewed from opposite sides of the normal to 
each picture, are projected upon retinal surfaces which are not planes, 
but nearly spherical, and hence are slightly dissimilar. 
The full description of the reversible stereoscope, and the geome- 
tric discussion of the new method of stereoscopy, may be found in the 
American Journal of Sctence for March and April, 1882, the London 
Philosophical Magazine for April and May, 1882, and the Popular 
Sctence Monthly for May and June, 1882, in which latter it will appear 
as an illustrated article. 
Feb. 20, 1882. 
LECTURE EVENING. 
The President, Dr. NEWBERRY, in the Chair. 
The hall was completely filled. A 
Mr. Wo. E. Hippen exhibited an extraordinarily large crystal 
of Monazite, from North Carolina. 
The second lecture of the regular monthly course was then de- 
livered, by Dr. J. S. NEWBERRY, upon 
THE ANCIENT CIVILIZATIONS OF AMERICA. 
(Abstract.) 
Two distinct civilizations have left their traces in different parts of 
North and South America: 1. That of the Mound-Builders in the 
Mississippi Valley; 2. That of the Stone House or Temple-Builders 
of the table-lands*of North America, the Isthmus, and the western 
coast of South America. ’ 
Of these the relationship is obscure, and no certain proof has been 
furnished of their synchronism or their genetic connection. 
(I.) The whites, on their advent, found the east coast of North Amer- 
ica covered with dense forests, and inhabited by wild animals and the 
nomadic Indians. It was only when the wave of migration had 
reached the basin of the lakes and the valley of the Ohio, and the 
forest was then cut off, that mounds, earthworks, mines, etc., were 
brought to light, which prove that this region had for ages been occu- 
pied by a numerous, sedentary, and partially civilized people. The 
date of their occupation of the Mississippi Valley cannot be accurately 
determined. Their works had been abandoned and overgrown by the 
