ZOOLOGY A.ND BOTANY, MICROSCOPY, ETC. 



377 



ground mirror-lens L, whose silvered surface is protected from injury 

 by being cemented on to a glass block A, provided with a suitable recess. 

 The stop B, T-shaped in cross-section, shuts oat the direct rays, and 

 those of N.A. less than I'D; it is cemented centrally on the under 

 surface of the mirror-lens. The glass plate P serves to protect the 

 whole arrangement from external effects : its ends are made to project 

 somewhat beyond A, so as to receive the stage-clamps. This instrument, 



z: 



j^ 



^ 



\ CREICHERTWIEM. / 



M 



*-■ D 



1X3 



^ 



2 



Fig. 100. 



listed by the manufacturer as " mirror-condenser E," is centred and 

 manipulated exactly as in figs. 97 and 98. 



In figs. 100 and 101 we have a more developed form of type E, 

 designed to satisfy the highest requirements. The lower glass plate is 

 replaced by a metal plate Z, whose projecting ends serve for the stage- 

 clamps. The obliquely ground plate A is pressed downwards by the fillets 



'Fig. 101. 



F. The plate D is perforated in the middle by an opening fitted in 

 with a window, which can be easily screwed out. Plate A bears on its 

 upper side two collars (fig. 101), which are intended to receive two smaller 

 clamps, Ko, by which means the preparation can be fixed on the con- 

 denser. The advantage of this form, known as " mirror-condenser F," 

 is that it can be taken to pieces for cleaning, and is better protected 

 from injury by the metal mounting. 



