The Mentor · The Story of the Lens · Page 10

PART OF SOLAR SPECTRUM
    The manufacture of camera lenses has become a highly specialized art, as rigidly exact and painstaking as the making of a large refractor. So large must be the output of these lenses that much of the hand grinding and polishing has long since been superseded by the motor-driven machine. And yet the skilled artisan is as indispensable as ever. The grinding is carried to an accuracy of one fifty-thousandth of an inch. Then, after a most critical inspection, each lens is centered in a lathe and mounted. The Microscope     If it may be said that the telescope has brought to our knowledge new worlds without end, so is it equally true that the microscope, penetrating the universe in the opposite direction, has revealed systems of life and matter as truly marvelous as the infinite depths of space.
    Until 1870 the compound microscope was a very imperfect instrument. Up to that time it had been built on the same general plan as the telescope. Its defects were fully appreciated, but no one knew how to remedy them. Then Professor Abbe of Jena, the master genius of modern optics, attacked the problem and successfully solved it. He corrected every aberration and designed an objective which is today the basis of all compound microscopes. In this objective are six lenses, the smallest of which is only one-sixteenth of an inch in diameter. The machinery for grinding it is a marvel in itself, and the grinding is done by trained technicians who have worked at the art from boyhood. They can tell by touch the progress of the work, and the finished product must be as perfect as the largest refractor.
    As the name signifies, a compound microscope gives double magnification. The objective itself frequently gives a primary magnification of 95 diameters, which is multiplied by the eyepiece to 1,200 diameters.

SETTING DISKS IN GRINDING SHELL

This is about the limit for practical work, although magnifications of 3,000 diameters are possible. Coupled with the camera and the arclight, the microscope gives the microphotograph. The value of the microscope to science can hardly be estimated. Biology, bacteriology, the causes of disease, a knowledge of the structure of metals and crystals, have all been made possible through its marvelous powers of penetration. The wave length of light, itself, has imposed a limit to these powers, and further magnification is impossible. But just as this crisis arrived the