Page:Popular Science Monthly Volume 72.djvu/67

 handle. With the late construction of the "cab" of the driver, the needs of the right eye were accentuated because the engineer in looking out of the window at his right hand is compelled to put no more than his right eye out of the cab-window. If he put the left eye out of the left-side window he would have to put the entire head out in order to see with the right eye. Thus right-eyedness has unconsciously compelled the driver to disuse the right hand for the naturally expert work with the throttle-valve, in order that the greater danger may be avoided that would follow both to the engineer and to his train, from putting the whole head out of the left window of the cab.

Among the many ocular problems of railway employees those relating to deficient color-perception are of great importance, but equally great are those regarding presbyopia or the failure of visual acuteness after 40 or 45 years of age, and especially should the diagnosis of right-eyedness or left-eyedness be held of prime necessity. The left hand may be allowed, somewhat against nature, to manage the throttle-lever, but the right eye must be the absolute judge of signals, etc. Undoubtedly there are a few hundred, at least, of left-eyed engineers, signalmen, etc., on our roads, and their disability for their peculiar calling is greatly endangering lives and property. Nor should it be forgotten that there are generally proportionally more left-eyed than left-handed men. As trolley-car "gripmen" or engineers, chauffeurs of automobiles, etc., the left-eyed are at only a slight disadvantage, because nothing is in front of their eyes to impede the dominant function of the right eye. Despite this fact the automobile chauffeur sits on the right-hand seat, not only because of inherited custom, but again that his right eye may have the slight advantage of position and that his right hand may be free to use in almost every instant's emergency. In our trolley cars and electric locomotives the all-important brake is operated with the right hand.

To epitomize, the resolution of the mysteries as to the origin of right-handedness and the rule of the road may be made only by grasping the phenomena as a whole, i. e., by massing the facts of the entire history from prehistoric savage battle and barter to the expert locomotive-engineer of to-day running a "limited" train at the rate of a mile or more a minute on a two-track or four-track railway. Even the cave men show that right-handedness was the rule in their time, and spear-hand, shield-hand, gesture-language, digital-counting, and the tally-stick, the world over, fixed the speech and writing and right-hand brain-centers in the left half-brain—and, of course, those of the left-hand and fingers in the right half-brain. War made up the life and set all the fashions of beginning civilization, and war together with narrow streets established the custom of right-hand passing, for walkers, riders of horses, asses, mules, etc., and for drivers of all