60 THE MICROSCOPE. 



objective, and if intended to be so used, the correcting 

 adjustment will be unnecessary, since the body part 

 can be made shorter, and the back lens brought into 

 close contact with the binocular prism. 



Messrs. Swift have also constructed a series of 

 object-glasses for a similar purpose. The taper front 

 objectives (fig. 36) are for use with their erecting 

 Stephenson's binocular instrument, and for the better 

 illumination of opaque objects. From their peculiar 

 construction, the illuminating rays from the bull's-eye 

 condenser are made to impinge somewhat more verti- 

 cally upon the object, thus avoiding deep shadows, 

 which often give rise to false appearances when the 

 light is thrown too obliquely on the object. 



FIG. 36. Swift's Taper Object-glasses. 



With regard to the binocular microscope, it should 

 be understood, writes Professor Abbe, that fairly satis- 

 factory stereoscopic observation cannot be extended 

 beyond moderate amplification, not even when the 

 binocular arrangement allows of the use of high 

 powers. In fact, as soon as the use of higher powers 

 is resorted to, stereoscopic vision is limited to objects 

 of so little depth that a merely plastic view of them 

 can hardly be productive of any scientific advantage, 

 although effective images may still be obtained. 



Resolving Power is the power or capacity of the- 

 objective to resolve the finest lines, striae or dots ; that 

 is, separate and define them distinctly. Resolution 

 increases with width of aperture, and may therefore be 

 regarded as another expression for definition. The 



