200 THE AMERICAN MONTHLY [June 



DIATOMS. 



The Marking on Diatoms. — Whipple's work on the Mi- 

 croscopy of Drinking" Water, says : 



"The valves of most diatoms are marked with lines or 

 points. In many cases the lines may be resolved into 

 series of points, pearls, beads, or striae, when a hig-her 

 power of the microscope is used. The variations in the 

 number and size of these points and their uniformity in 

 different individuals of the same species make them con- 

 venient objects for testing- the resolving- power of micro- 

 scopes. The variation in the number of these striae may 

 be seen from the following- table : 



Number of Strije per Millimeter. 



Long-itudinal. Transverse. 



Epithemia ocellata, Kz 800 430 



Navicula major, Kz 850 630 



Navicula viridis, Kz 2400 720 



Navicula lyra 850 1,000 



Cymbella navicula,Ehr .1,200 1,500 



Pleurosig-maang'ulatum,Sm . . 1,580 2,100 



Synedra pulchella, Kz 680 2,150 



Navicula rhomboides 1,700 2,700 



Amphipleura pellucida, Ktz . . 3,400 3,700 to 5,200. 



NEW PUBLICATIONS. 



The Prang Standard of Color. — This is a book g-iving^ 

 in print 1176 different standard color-fields, arrang-ed in 

 monochromatic and polychromatic scales on 7 plates, 10 x 

 14 inches, under a simple and direct system of nomencla- 

 ture, permitting- the precise desig-nation of any color and 

 indicating- at the same time its composition. Supplemen- 

 tary text explains the work and its use. Colorists, Art 

 Teachers, Art Students, Manufacturers, and users of col- 

 ored materials. Stamp Collectors, Color Printers, etc., 

 should possess this work. Price 50 cents, published by 

 Louis Prangs, Boston, Mass. 



