84 



DIATOMS. 



Mr. J. D. Moller, of Wedel, in Holstein, Germany, at 

 the suggestion of a friend made the first so-called type- 

 plate of diatoms. On this slide the forms are arranged 

 in rows and can be catalogued, and any particular form 

 readily found even under a high power. This first 

 slide was made in 1867, and hundreds of them have been 

 made and sold by this preparer since. It was a long 

 time before any one else attempted to duplicate this dif- 

 ficult work, but now several men make and sell them, but 

 none of them have ever equalled the beauty of Holler's 

 best work. It is simply perfect. This gentleman, after 

 five years' patient work, got together the materials for the 

 greatest diatom slide on record. It took him forty days 

 to place the forms in position, but he finally succeeded in 

 getting the mount completed. The diatom group is 

 gmm. ^j g^ jjj gj2;e and is divided into 9 squares, with 133 

 rows, containing 4,026 different species and varieties. 

 He hopes to sell it to some rich man or museum and 

 wants about $10,000 for it, I believe. The type-plate I 

 show here to-night is not one of Moller's and contains 

 only 100 species. They are selected mainly for their 

 beauty and are generally large forms. 



Of what use are diatoms ? As I have already stated, 

 they purify the water for animal life. They also furnish 

 food for myriads of small creatures which are in their 

 turn devoured by a higher class of organisms. 



In the fossil state they have various uses in the arts — 

 dynamite, packing for boilers, steam pipes, etc., to pre- 

 vent radiation of heat. But the diatom under the micro- 

 scope has led to the most important and brilliant results. 

 On account of the fineness of the striation of various 

 species they are used as test objects to determine the de- 

 fining or resolving power of any objective. For a long 

 time no human eye had seen the lines on amphipleura 

 pellucida, but by analogy the lines must be there, unless 

 it should prove a remarkable exception to all its race, and 



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