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 

 "Acme," made by J. W. Sidle & Co., of Lancaster, Pa. This 

 instrument, in its monocular form, was, we believe, arranged by 

 Prof. J. Edwards Smith, and the details of its construction were 

 worked out with special reference to the use of objectives of 

 high angles. So far as this purpose is concerned, the "Acme" 

 has many points in common with the "Biological" stand of 

 Mr. Bulloch, the " Histological " of Zentmayer, and the "In- 

 vestigator" of the Bausch & Lomb Optical Co., the differences 

 being chiefly in details of construction, which leave room for 

 choice on the part of intending purchasers. We therefore turn 

 to the binocular feature as being that with which we are now 

 more immediately concerned. 



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 

 Wenliam prism. In some forms of the Acme binocular the 

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

 fore with wide-angle lenses of low power. 



