OF OPTICAL INSTRUMENTS. 



Ill 



FIG. 1162. 



1198. Improved Achromatic and Tinted Condenser, of 90 degrees angular aperture ; 

 constructed as a perfect substitute, at a moderate cost, for a large number of the 

 separate pieces of illuminating apparatus ; it is also an excellent sub-stage, so 

 essential to the compound microscope, and is applicable to all microscopes 

 having sufficient depth beneath the stage. It is suitable for all objectives from 

 the 2 inch, to the one-fifth, and is tinted for correcting the yellow rays of artificial 

 light ; with rack and pinion motion for focussing, and is an excellent spot lens ; 

 large diaphragm with rotating cap, in which are fitted three discs for stops for 

 oblique light, small diaphragm of apertures, polarizing prism, selenite dia- 

 phragm with two selenite films and clear aperture, for illuminating with low 

 powers . . . . . . . 4 12 6 



1199. Or with parabola 



' 5 10 



1200. An extra combination of 135 degrees angular aperture can be adapted for use 

 with powers from 1 inch upwards ... 1 10 



1902. Improved Achromatic Condenser, with diaphragm for dark ground and 

 oblique illumination, being a modification of No. 1198 2 15 



