THE STEPHENSON BINOCULAR. 33 



who delight in showing this imperfection as one of the 

 beauties of the binocular microscope. 



It will thus be seen that objectives of higher amplifica- 

 tion than the half-inch cannot be satisfactorily used with 

 the binocular, and even the half-inch requires making of 

 specially small aperture to adapt it to this use. The 

 prism is always made removable, so that at any time the 

 microscope can be used as a monocular by simply with- 

 drawing it. 



In order to enable observers to use binocular vision with 

 high powers, Messrs. Powell and Lealand have devised a 

 system of prisms which may be used with objectives as 

 high as the -$ The images produced are not stereoscopic, 

 but exactly similar. Mr. Wenham has also devised prisms 

 for using high powers binocularly, which appear to act in a 

 very successful manner. 



Tolles, of Canastota, U.S., makes a binocular eye-piece for 

 the ordinary single body, which gives a large and well-illu- 

 minated field with low and medium powers. Professor 

 H. L. Smith remarks that he has used the ^ and ^ 

 objectives with it. 



Another binocular microscope was devised some years 

 ago by Mr. J. W. Stephenson, which has since been success- 

 fully made by Mr. Browning. Within the last few years 

 the cost of this instrument has been considerably reduced, 

 Messrs. Swift and Son and Mr. Baker having each con- 

 structed a Stephenson binocular for dissecting purposes at 

 the moderate price of //. 



The Stephenson binocular, as made by Mr. Browning, is 

 shown at Fig. 19, in which the change from binocular to 

 monocular or vice versd can be effected without unscrewing 

 any part or interfering with the object under examina- 

 tion. 



In this form of binocular the rays are divided by two 



D 



