INDUSTRIAL PROGRESS DURING THE YEAR 1874. xxxix 



other hand, he maintains that sound is transmitted with 

 great facility through the atmosphere when charged with 

 fog, by reason of the more uniform distribution of heat and 

 moisture in the atmosphere when in this condition. 



But the explanation of these phenomena by Professor 

 Tyndall has not generally been accepted by men of science. 

 Thus Professor Henry, the chairman of our own Light-house 

 Board, and Professor Reynolds, of England, are of the opin- 

 ion that the cause of the feeble intensity of sounds often ob- 

 served, even when they are transmitted through a clear 

 atmosphere, is owing to the different velocities with which 

 air moves at the ground and at an elevation above it. Hence 

 when the wind moves with the sound it will tilt the sonorous 

 wave-front downward, and the observer on the ground, or 

 near the surface of the sea, will hear the sound more dis- 

 tinctly even than when the air is still ; but if the wind move 

 against the sound, then the sound passes over the head of 

 the listener. Professors Henry and Reynolds have inde- 

 pendently brought their views to the test of a rigorous 

 course of experiments, and they find that the facts conform 

 to their hypothesis. The reader is referred to accounts of 

 these important researches, contained in the body of this 

 volume. 



Professor A.M.Mayer continues his researches in acoustics, 

 and has this year published papers Nos. 5, 6, and 7 of his 

 investigations on this subject. He has brought forward a 

 new theory of the mode of audition in man and mammals, 

 which he arrived at after a minute study of the anatomy of 

 the ear. He is of the opinion that the fibrils of the auditory 

 nerve must vibrate one half as frequently as the membrane 

 of the drum of the ear, or as the basilar membrane which 

 forms the floor on which rests the organ of Corti. His hv- 

 pothesis is supported by experiment, for he finds, when vi- 

 brations of a tuning-fork are sent directly into the inner ear 

 through the bones of the head and therefore when the nerve 

 fibrils must of necessity vibrate as often as the fork that 

 the note of the fork rises an octave above what is perceived 

 when the fork vibrates the air outside the ear. This pre- 

 diction from his hypothesis has been confirmed by some of 

 the best-educated ears. 



In another research, Professor Mayer shows by very simplo 



