594 



Marvels of the Universe 



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[A. E. Smith. 



A TRIANGULAR DIATOM. 



This Diatom is here enlarged to 500 times its natural dimensions, a scale of 

 magnification which resolves the central dots into six-sided openings. 



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[A. E. Smith. 



A CUSHION-SHAPED DIATOM. 



A nearly square Diatom, closely related to the one shown above, magnified 



440 times. 



magnification that is required 

 to effect this resolution is verj' 

 great, in the original negative 

 amounting to about three thou- 

 sand eight hundred diameters, 

 an amount which, if applied to a 

 man, would raise his stature to 

 over four miles, and if a half- 

 penny were magnified the same 

 amount would extend it to over 

 three hundred feet. 



These interesting little bodies 

 really consist of two \'alves 

 (united by a kind of band), one 

 overlapping the other much as 

 a lid of an ointment-box covers 

 the box itself. They are dis- 

 tributed in a living state all over 

 the world, in ditches, ponds, 

 lakes, rivers and seas, ha\'ing 

 even been found in the Arctic 

 ice ; and as fossil remains they 

 are found sometimes in great 

 heaps in many parts of the 

 world ; the city of Richmond, 

 ^'irginia, for example, being 

 built on a laj'er of fossil Dia- 

 toms over fifteen feet in thick- 

 ness. Diatomaceous earth — as 

 the material is sometimes called 

 — is to be found in Great Britain 

 at Peterhead, Dolgelly, Lough 

 j\Iourne, Raasay, Cantj're, Mull, 

 and other places. Fossil Dia- 

 toms, too, have been found in 

 volcanic dust. 



Some of the comparatively 

 large varieties are composed of 

 very marked dots as secondaries, 

 one being shown in the illus- 

 tration at foot of page 392. 

 Others are circular in form, as 

 seen in the illustrations on page 

 393, the lower reminding one of 

 a spider's web. Boat-shaped 

 varieties are furnished by later 

 illustrations, whilst the honey- 

 comb or cavity type of second- 

 aryj structure is displayed on 



