68 W. HISLOP ON OBLIQUE ILLUMINATION. 



able tenacity to the glass. This disc is then mounted, objects 

 downwards, on the ordinary wooden slide, with a large well 

 chamfered central opening, and secured either by a slip of paper, 

 by another slide superposed, or any other convenient means. 

 (Fig. 6, pi. 4:.) The surfaces exposed to light should be coloured a 

 dead black. If laid object downwards in the drawer, no dust can 

 fall on the preparation, or it may be covered, if thought desirable, 

 by a small envelope when out of use. 



I regret that want of time has prevented me from completing 

 a course of comparative examinations of various structures under 

 the conditions 1 have endeavoured to describe. 



At a future meeting I may probably be able to state the result of 

 these observations. 



