plane the pilot must know how far he is above the ground (even to a matter of inches, for expert handling) as the wheels skim over the surface of the field before they touch. Just so must a good automobile driver be able to appraise the “holes” in traffic through which he must guide his car without bumping the other fellow.
The depth perception test is made with the applicant sitting about twenty feet in front of a box-like object. Through a small window he sees two upright sticks like miniature goalposts. To one is attached a string which pulls it forward or back. The examiner separates the “goalposts,” and the applicant must adjust them so that they seem to be on a line with each other and equidistant from him. Inability to bring them together within the limit of a few millimeters often ends a flying career before it has begun.
A candidate who ultimately seeks only a private license can “get by” with physical imperfections that would make him ineligible for a higher grade. The necessity for wearing glasses, for instance, would disqualify him except in the private classification, and he would be passed for that only if the correction in his lenses was not too great.
Once a license is granted, a pilot is subjected to periodic examinations to keep his rating. This requirement is for checking on physical condition, as well as recording how much flying is being done. If some such practise were followed with automo-
