52 



Modern Microscopy. 



We show (Fig. 14) one of these condensers mounted 

 for sub-stage, with iris diaphragm, by means of which the 

 aperture may be quickly and exactly obtained. This is a 

 most convenient method of fitting, and stops are supplied by 

 means of which dark ground illumination may be obtained, 



FIG. 11. Abbe Illuminator, 

 1-20 N.A., optical part. 



stage Instrument. 



FIG. 12. Achromatic Condenser, 

 I'O N.A., optical part. 



as" with the spot lens de- 

 scribed on page 56, also 

 blique illumination for the resolu- 

 tion of Diatomaceae, etc. This latter 



P<* d > haa bee condemned by 

 several leading microscopists, but 



FIG. 14. Iris Diaphragm, as fitted to Abbe Illuminator, etc. 



as it is always some satisfaction to the amateur to show 

 striae, etc., on Diatomaceaa in as clear a way as pos- 

 sible, and to be certain always of obtaining the same 

 result, he would be well advised in having the clia- 



