Trans. N. V. Ac. Set. 1 'iO Feb. 20, 



angle formed by the planes of the cards on which the pictures have 

 been have made. 



Mr. Sj'EVENS 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 

 America^i [ournal of Science for March and April, 1882, the London 

 Philosophtca/ Magazine ior A\)n\ and May, 1882, and the Popular 

 Science 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. 



Mr. Wm. E. Hidden 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: i. 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 he accurately 

 determined. Their works had been abandoned and overgrown by the 



