MICROSCOPIC ACCESSORIES. 3 



handle, so as to narrow the aperture, accomplishes the 

 end most perfectly. (Fig 10.) 



FIG. 10. 



Collins's Now (jrr dilating Diaphragm. 



Beck's Iris Diaphragm, is a further improvement of this 

 sort. 



Condensers. The loss of light resulting from the em- 

 ployment of high powers has led to several plans for con- 

 densing light upon the object. Sometimes a plano-convex 

 lens, or combination of lenses, is made to slide up and 

 down under the stage. A Kellner's eyepiece, or some 



FIG. 11. 



Smith and Beck's Achromatic Condenser. 



similar arrangement, especially if fitted with a special 

 diaphragm, containing slits and holes, some of the latter 

 having central stops, is of very great use. First-class in- 

 struments are fitted up with achromatic condensers (Fig. 

 11), carrying revolving diaphragms, some of whose aper- 



