USE OF THE MICROSCOPE. 



57 



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

 ward with the j'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 ^o^ n f a 

 millimetre, and the markings on Grammataphora subtilis- 

 sima at 32 to 34 in the same distance. 



FIG. 31. 



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. 



