136 



PROGRESS OF MICROSCOPICAL SCIENCE. 



Grade of 

 Difficulty. 



Test. 



Balsam 

 I or Dry. 



Minimum Power 

 of Objective. 



VII. 



YIII. 



IX. 



X. 

 XI. 



xir. 



XIII. 



. XIV. 

 XV. 

 XVI. 



XVII. 



XVIII. 

 XIX. 

 XX. 



Stauroneis Pha-nicenteron 

 Pleurosigma baltieuin 

 Grammatophora marina . . 



Synedra splentlens 



„ fulgens 



Pleurosigma attcnuatum . . 



Synedra pulchella 



Pleurosigma angulatum . . 

 „ acuminatum 



Nitzscliia sigmoidea 



Surirella gemma (transverse) . . 



»J 77 »> 



Nitzschia ampliioxys 

 Pleurosigma strigosum . . 

 ,, Spencerii 



„ angulatum .. 



77 1) 



Nitzscliia sigmoidea 



Grammatophora subtil issiui a .. 

 Cymatopleura elliptica 

 Pleurosigma fasciola 

 Surirella gemma (longitudinal) 



>» » 



Frustulia saxonica 



Nitzschia curvula 



Amphipleura pellucida . . 



D 

 B 

 D 



7? 



B 

 D 



D 



Direct Light. 

 H., VII. — N., m. 



H., vm. 



77 

 »7 



Z.,F. 



H., IX., X. 



■ N., V. 



77 



-N.','v. 



77 



- G., VII. 



Oblique Light. 



N., V. — Z., F. 



Direct Light, 

 H., IX., X. — G., VII. 



Oblique Liglit. 

 H., VII., VIII. — G., v., VI. 

 H., IX. — G., VII. 



77 >7 



H., X. — „ 



Artiiicial Light. 

 H., X. — G., viT. 



Monochromatic I^ight. 



H., vn. — G., v. 

 H., IX. — Z., F. 



H., X. — G., VII. 



Table II. — Grade of Penetration. 



Objective. 



Gundlacb I. 



Nachet O. 



7 I- 



Gundlach ' II. 



ni. 



IV. 



Hartnack IV. 



Nachet V. 



Hartnack VII. 



Gundlach V. 



VI. 



Hartnack VIII. 



Zeiss F. 



Hartnack IX, 



X, 



Powell and Lealand , . ^ 



(^immersi07i) 



Gundlach VII. 



VIII. 



:: ;: :: ;: ;; ^ 



Oblique Light 



