Where large numbers of people are employed, it is comparatively easy
to use tests for discovering defects of sight or hearing by simple
apparatus without requiring the services of a high-priced expert. By
adopting these test methods any manager of a large industrial
establishment can satisfy himself whether his employees are up to
certain normal standards. He can even apply the tests to himself.

Optical tests can be conducted by securing an ordinary letter chart
such as is used by oculists and opticians. Seat the subject twenty
feet away. If he can read all the lines of letters from the largest
down to the smallest his eyesight is practically perfect. In a large
percentage of cases the smaller lines of type are blurred and
invisible. To detect the cause and degree of defects of the eyes it is
necessary to try out the eyes by using a trial spectacle frame and
inserting detached lenses before the right eye and the left eye
alternately. One of the most common forms of defective vision is
astigmatism. A chart has been designed with a series of circles and
straight lines radiating from the center. If the subject is astigmatic
he will see some of the straight lines distinctly while others will be
blurred. For instance, one or two of the vertical lines may appear
very black and strong while all others will look like a hazy network.
This defect, due to unevenness of the spherical surface of the
eyeball, is easily corrected with properly ground glasses.

Defects in hearing can be easily determined by means of an
"acoumeter." This little instrument measures the acuteness of the
hearing very accurately by means of shot dropped from varying heights
upon strips of glass, copper and cardboard. Tests with this device
indicate whether the subject's hearing is above or below normal.