PLATE 16. 



Photomicrography of Geological preparations. 



A SECTION OF PITCH STONE x 60 



Objective Leitz No. 3 Achromat. 16mm. N.A. 0.3. 



Ocular Leitz 0. 



Condenser ... Watson's Universal Achromatic. Stopped down. 



Illuminant ... Liliput 4 amp. arc. 



Aux. Condenser Double convex lens, giving parallel beam. 



Screen Wratten's B (green) and E (orange). 



Plate Wellington Anti-Screen. 



Exposure 1 min. 



The section of Pitchstone was rather thick, and in order to get 

 depth of focus the substage iris was closed down to about a quarter of 

 its full aperture. This, together with the use of the two screens 

 B and E, necessitated a comparatively long exposure. 



B TRANSVERSE SECTION OF FOSSIL WOOD (Lepidodendron selaginoides) 

 x 13, from Halifax. 



Objective Seibert's Achromat. 36mm. 



Ocular None. 



Condenser ... Abbe with front lens removed. 



Illuminant ... Liliput 4 amp. arc. 



Aux. Condenser Double convex lens, giving parallel beam. 



Screen Green glass. 



Plate Ilford Chromatic. 



Exposure 4 sec. 



Developer ... Pyro-formosulphite. 



Photos. W. B. R. 

 H. L. H. 



I To follow page 144. 



