64 POPULAR SCIENCE MONTHLY 



vehicles, and for vessels. For walkers and vessels no people ever 

 changed the custom, but especially the English, while preserving right- 

 hand passing in foot-passengers and on the sea, anomalously developed 

 left-hand passing for vehicles, and the same, of course, for double- 

 track railroads. What everybody has failed to see is that right- 

 handedness is necessarily bound up with right-footedness, and right- 

 eyedness, because all closely united functions of the body must be 

 correlated and their centers of motion located in contiguity and upon 

 one side of the brain, in order to make effectual and rapid all re- 

 sponses of the organism to circumstance or environment. This works 

 toward a necessary and desirable differentiation of function that 

 makes the aims of the " ambidexterity " sillies more than result- 

 less and foolish. Because whenever a center or congress of centers 

 is developed in one half-brain, disuse and transfer to the other half is, 

 according to age, either impossible, faulty, handicapping, or disease- 

 producing. Coordinated functions of the body require coordinated 

 and contiguous nerve-centers upon the same side of the brain, at least 

 so far as is possible. If one or two dextral factors are in opposite 

 cerebral hemispheres, responsive and quickly-acting coordinated func- 

 tions will be slower and more inaccurate than if on a single side. The 

 English left-hand passing of vehicles is probably due to the influence 

 of the single-hand fights on foot, tourneyings and joustings of horse- 

 back riders, in which meeting and passing to the left was inevitable. 

 The custom grew and continued directly into that of the wagon- 

 drivers. In the United States there was a reversion to the right-hand 

 passing of vehicles, because of the abeyance of left-hand passing of 

 vehicles, and of vehicles themselves, for so long, with growth of the 

 natural right-hand passing by walkers, horseback-riders, ox-teams, and 

 wagons with drivers on the near-wheel horse, such as is found in the 

 later prairie-schooner, and six-mule army-wagon. Three double-track 

 railways in the United States still pass their trains to the left, an 

 absurd and bad custom, expensive and productive of wrecks. But 

 despite this the enginer sits upon the right of his cab, because he can 

 in this place better observe the track and signals in front and to his 

 right, and with the dominant right eye only outside of the cab-window, 

 whereas, if sitting on the left, he would be compelled to put the entire 

 head out in order to see with the right eye, and, even then, because of 

 the boiler, not so well. Only right-eyedness will explain the long, 

 doubtful, and varying custom in engine-building as to the position of 

 the engineer in the beginning of history of railway construction and 

 signaling. 



