USE OF THE MICROSCOPE. 



57 



to 130,000 in an inch. It has been resolved by Dr. Wood- 

 ward with the y'gth immersion of Powell and Lealand, 

 using oblique sunlight through a solution of ammonio- 

 sulphate of copper. 



The longitudinal lines (between the transverse) of the 



FIG. 30. 



Valve of Surirella Gemma, 

 a. Transverse ridges. 6. Longitudinal lines, c. The same, resolved into areolations. 



Surirella gemma are estimated at 30 to 32 in T J<jth of a 

 millimetre, and the markings on Grammataphora mbtilis- 

 sima at 32 to 34 in the same distance. 



FIG. 31. 

 a. 



Grammataphora Subtilissima. 

 a. Valve. 6. Transverse lines. 



J. D. Moller has produced a very excellent test-plate, 

 containing twenty diatoms, with descriptions, according 

 to their value as tests. 



