138 



TESTING THE MICROSCOPE. 



We may, however, specially mention the test-plates of Moeller r 

 consisting of twenty diatoms arranged in a row, according to the 

 difficulty of their resolution. The names of these diatoms are : 

 1, Triccratium Favus ; 2, Pinnularia nobilis ; 3, Navicula Lyra 

 var. ; 4, N. Lyra ; 5, Pinnularia interrupted var. ; 6, Stauroncis 

 Phceniccnteron ; 7, Grammatophora marina (more coarsely marked 

 than those of Bourgogne) ; 8, Pkurosigma balticum; 9, P. acmni- 

 natum ; 10, Nitzscliia amphioxys ; 11, Pleurosiyma anyulatniu ; 

 12, Grammatophora occanica suUilissima (marina} ; 13, Surirdla 

 Gemma, (for transverse lines) ; 14, Niztscliia sigmoidea ; 15, Pleuro- 

 siyma Fasciola var. ; 16, Surirdla Gemma (for longitudinal lines) ; 

 17, Cymatopleura elliptica ; 18, Navicula crassincrvis, Frustulia 

 saxonica ; 19, Nitzschia curvula ; 20, Amphipleura pellucida. 1 



For convenient comparison of organic test-objects with the images 

 of wire-gauze and of Nobert's test-plates, we add a table of the 

 distances of the lines according to measurements made by Dippel, 2 

 Flcegel, 3 and Abbe. 



The two last-named test-objects, Frustulia saxonica and Amplii- 

 pleuri pellucida, are clearly amongst the finest and most difficult 

 tests with which we are at present acquainted ; but that in 



1 Moeller supplies also diatom type-plates with 100 to 400 objects, arranged 

 systematically in rows. 



2 "Das Mikroskop," p. 134. 



3 " Botanische Zeitung," 1869, p. 741, 



