JOURNAL OF MICEOSCOPICAL SCIENCE. 



DESCRIPTION OF PLATE X, 



Illustrating Dr. Royston-Pigott's paper on Higli-Power 

 Definition and its Difficulties ; and the Visibility of 

 Diatomaceous Beading. 



Fi"-. 



a. iQ. 



1 and 2. — Longer and shorter black lines of interference according to the 

 less or greater angle of intersection of ribbing forming Podura 

 waviuess. 



3. — Delusive lines formed by beading imperfectly defined in diatoms and 

 in scales, as in Figs. 6, 7, 8. 



4 and 5.— Hexagon shadows developed by ill-defined spherules. 



9, 10, 11, 12, and 13. — A variety of appearances shown by diatoms 

 according to their treatment ; the nature of the objectives and the 

 direction of the light. 



14. — Section of beading of scales arranged in many cases in close contact. 



J 5. — Black shadows of intersecting superimposed beading. 



16. — Their accepted though erroneous appearance, as in Podura curvicollis 



test scale. 



17, 18, and 19. — Observed diffraction, causing broken lines when fine 

 parallel lines intersect with a small space between the planes in 

 which they lie. 



