From the February 5, 1938, issue

DIATOM SHELL MARKINGS TEST QUALITY OF LENSES

Diatoms, tiny one-celled water plants of a myriad forms, have long been standard test objects for microscopes. The exceedingly fine sculpturings and markings on their silica shells defy any but good lens combinations to bring them into sharp definition. On the cover of this week’s Science News Letter is the picture of one, a wheel-shaped form, taken with a new small-camera photomicrography set-up developed in the Kodak Research Laboratories.