PLATE 23. 



Dark Ground Illumination of Transparent Objects. 



A wheel stop placed beneath sub-stage condenser. 



A FAIRY FLY x 50 



B GROUP OF SPONGE SPICLLES x 50 



Objective Leitz No. 3. 16mm. Achromat. 



Ocular Leitz No. 3. 



Condenser ... Abbe, with \vheel stop. 



Illuminant ... Limelight. 



Aux. Condenser Zeiss Kohler condenser, parallel light. 



Plate Warwick. 



Exposure 5 sec. 



Developer ... Pyro-soda. 



Davis nose-piece diaphragm used. 



Photos. W. B. R. To follow Plate 22 and page 176. 



