68 



PRACTICAL MICROSCOPY. 



plano-convex lens about ij inches in diameter, its flat side 

 being placed next to the object, and surmounted by a 

 smaller lens of the same form (hemispherical). A very 

 oblique illumination is possible with this condenser, and as 

 made by Messrs. Ross and Co. it is shown in Fig. 45. 



Several makers are now producing oil-immersion con- 

 densers, in which the under side of the slide is connected 

 with the condensing lens by means of a film of castor oil, 

 oil of cedar wood, or glycerine. That made by Messrs. 



FIG. 45. FIG. 46- 



Powell and Lealand is shown in Fig. 46. It is not achro- 

 matic, but is able to utilise rays of 130 balsam angle. 

 Beneath the lens are fitted diaphragms of peculiar pattern, 

 and by its use the most difficult test objects may be re- 

 solved with the mirror in the optic axis of the microscope. 



Messrs. Watson and Sons of Holborn produce an oil- 

 immersion condenser, in which the lens is mounted on a 

 plate of ebonite ; the object slide being placed above it, 

 the latter is held in position by a pair of clips, and is then 

 ready for examination. 



The swinging substages of Messrs. Ross and Beck are 



