332 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



121) as having said: "We who have dealt with the finitely small liv- 

 ing things have, perhaps, as much a sense of the highly complex, 

 unfathomable, the eternally elusive in the universe as do those who 

 look for the outer boundaries of space. Each group contributes a 

 different story of the same final significance." 



3. TECHNICAL AND INDUSTRIAL SIGNIFICANCE OF DIATOM SHELL 



STRUCTURE 



It will be readily perceived wdiy these varied forms of delicate 

 but strong, hollow, boxlike shells, composed of a resistant and inactive 

 material, in the form of thin walls and with a tremendous amount 

 of exposed surface, may have many advantages for industrial uses 

 because of these peculiar qualities. Their small size, for instance, 

 together with their great porosity, makes it possible for them to be 

 closelj^ compacted and yet to possess an astonishing amount of pore 

 space. This porosity renders compact masses of diatomaceous earth, 

 composed almost wholly of the shells of diatoms, exceedingly light 

 in weight, sometimes only one-sixth to one-ninth as heavy as water, 

 or as low as 8 pounds to the cubic foot, although silica, of which it 

 is composed, weighs twice as much as water, or 130 pounds to the 

 cubic foot. The remainder represents air space, amounting some- 

 times to as much as nine times the actual amount of shell substance 

 present. (See pis. 8 and 9.) 



The very fine and precise structure of diatoms early found utility 

 in scientific work in the recognition of its excellence as an object 

 for testing the quality of high-power microscope lenses. Among the 

 diatoms a sufficient range in size permitted the selection of various 

 species adapted for the testing of each different power of lens, the 

 structure in each case being on the border line of visibility for the 

 particular lens to be tested, so that a lens of good quality would re- 

 solve it while one of poor quality would not. Nothing has subse- 

 quently proved more suitable for this purpose. 



Lately a professor of the physics department of the University of 

 Illinois, seeking a fine, open mesh-work support or grid for the very 

 delicate metallic films only one to a few atoms thick which he was able 

 to produce and which he intended to bombard with other atoms in re- 

 search studies on the structure of atoms, looked naturally to the fine 

 porous shell of the diatom as the thing which might most readily 

 meet his requirements. What was needed w^as a fine sievelike screen 

 to support the film and yet provide free, open space for the unham- 

 pered passage of a stream of atoms directed against the film. In 

 answer to this rather unique request for the cooperation of the dia- 

 tomist, it was possible for our laboratory to select for him such types 

 of diatoms as would conform to his specifications. Thus it is impos- 



