OF THE MICROSCOPE. 57 



both eyes is very great, and the view which is obtained of any ob- 

 ject is so much clearer and more realistic, that we at once per- 

 ceive, by our .mere sense of vision, those features which we would 

 otherwise have to work out by tedious mental processes. It has 

 been said by some that the binocular is apt to exaggerate the 

 stereoscopic effects, and give false views. This is certainly not 

 the case under ordinary circumstances, and we doubt much if 

 it ever occurs. 



"We have selected as an illustration of the binocular micro- 

 scope, one of moderate cost, which combines the binocular 

 feature with those peculiar to the new American model the 

 United States Army Hospital Stand, made by Zeutmayer of 

 Philadelphia. The details of this stand have been worked out 

 with special reference to the use of objectives of high angles. 

 The substage, which carries the accessories and the plane and 

 concave mirrors, swings in the same manner as in the well- 

 known American Centennial Stand of the same maker, having 

 the object as its center, even when swung over the stage for 

 illuminating opaque objects, thus making a bull's-eye con- 

 denser unnecessary. It is provided with a graduated circle, 

 not shown in the engraving, for registering the degree of 

 obliquity, and a stop to indicate when it is central with the 

 main body. 



The binocular in general use, being that in which the Wen- 

 ham prism is used, consists of a main body through which the 

 half of the rays transmitted by the objective pass directly to the 

 eye-piece. In the figure (Plate VI) this body is the one nearest 

 to the reader, and connected with it is another body, through 

 which the other half of the rays pass they being diverted in 

 this direction by the prism, which, when in place, cuts the cone 

 of rays from the objective in two. The frame which carries 

 this prism is seen just above the point at which the objective is 

 attached, and it is so arranged, that when desirable it may be 

 drawn out, and thus the prism becomes inoperative, and the in- 

 strument is practically converted into a monocular one. This 

 is one of the important advantages which are peculiar to the 

 Wenharn prism. In some recent forms of the binocular the 

 entire fittings of the prism may be removed, so as not to inter- 

 fere with the wide-angle lenses of low power. 



