PRACTICAL MICROSCOPY. 



and under their new twelfth objective the result was 

 superb. 



This method of vertical illumination does not answer so 

 well with covered objects mounted dry ; there is a misti- 

 ness produced by the reflection from the covering glass, 

 while with objects mounted in balsam the illumination is 

 perfectly satisfactory. 



The illuminator made by Tolles, and called the 

 " interior illuminator," may be seen in enlarged section at 



Fig. 56. A prism is inserted 

 between the combination of 

 the objective, which collects 

 and throws down the light 

 through the objective on to 

 the object below. The curves 

 of the lenses figured form 

 that celebrated \ upon which 

 there was so much contro- 

 versy as to the real aperture 

 some few years since. 



Another simple method 

 for illumination under high 

 powers was described by Mr. 

 James Smith at the March meeting of the Royal 

 Microscopical Society, 1880, extremely well suitable to 

 such objects as Podura scales, diatoms, &c., under powers 

 as high as the T^. 



Mr. Smith uses the bull's-eye condenser only, and places 

 it with the plane side uppermost, just above the stage, 

 the lamp being set in front at a distance of two or three 

 inches. The light enters the condenser, and is reflected 

 very obliquely upon the slide from the plane surface of the 

 bull's eye. 



An appliance often used to effect dark-ground illumina- 



FIG. 56. 



