National Geographic : 1918 Jan
(© Paul Thompson WHERE TIE MEDICAL EXAMINER USES A STOP-WATCH INSTEAD OF A STETHOSCOPE After a whirl in a revolving chair, each candidate for America's fly ing service is tested to see how quickly he recovers his equilibrium. The eyes are the index to man's balancing apparatus ©Paul Thompson SUBJECTING THE PROSPECTIVE AMERICAN AIRMAN TO THE FALLING TEST The sixth sense-that of equilibrium-is afunction of the labyrinth of the internal ear. Onepart of the labyrinth consists of three semi circular canals; set in different planes. Through these flows the endo lymph, a fluid which actslike aspirit-level.