MESSRS. SWIFTS CONDENSER. 67 



glass, made and sold by most opticians. The complete 

 condenser of Messrs. Swift and Son is a very ingenious 

 piece of apparatus ; it is made to supply the place of a 

 substage with all the ordinary compound substage ap- 

 paratus. It comprises an achromatic condenser with an 

 aperture of 140, a spot lens, a contracting diaphragm, 

 a revolving diaphragm and set of stops, polarising prism, 

 together with revolving mica and selenite films. The 

 polariscope is mounted on an eccentric arm, so that it can 

 be thrown in and out of use instantly, which is an important 

 feature, for it may be presumed that the polariscope would 

 be much oftener employed if it could be put in and out of 

 action as easily as shown in Fig. 44. 



FIG. 44. 



In the microscope itself Mr. Swift now inserts the 

 analysing prism of the polariscope in a brass box over 

 the Wenham prism, thus facilitating its use, as there is no 

 unscrewing of parts to fix the analyser in position. 



Reade's double hemispherical condenser consists of a 



F 2 



