The "human dynamo" is a man who long ago learned the lesson of scientific management of his own mental forces. He does one thing at a time, and does it the best he knows how. He directs the whole power of his mentality to the one problem and solves it with accuracy and dispatch. There is no more of a "load" on his "gray matter" than there is on that of the fretting, fuming, finger-biting fritterer, but every pound of steam is spent in useful work. Look at the victim of St. Vitus' dance. There you have an illustration of wasted energy. And it is mental energy, for every muscular movement represents the release of thought power. The mental lives of most men are equally aimless. They are lives of ceaseless activity producing nothing. [Sidenote: _Psychological Causes of Waste_] Sometimes it happens that a man is not working to advantage because of some defect in his physical make-up. He may have defective vision or some peculiarity of hearing that renders him unable to respond as quickly as he should to the demands made upon him. If these defects are ascertained, it is usually a simple matter to correct the defects by mechanical means or readjust the relative duties of different persons so that the defects will be minimized. [Sidenote: _Tests for Sensory Defects_] 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.