108 Bayleigh's Address to the British Association. 



satisfactorily explained. It has been proved that when proper 

 precautions are taken we are unable to distinguish whether a 

 pure tone (as from a vibrating tuning-fork held over a suitable 

 resonator) comes to us from in front or from behind. This is 

 what might have been expected from an a priori point of view ; 

 but what would not have been expected is that with almost any- 

 other sort of sound, from a clap of the hands to the clearest vowel 

 sound, the discrimination is not only possible but easy and instinc- 

 tive. In these cases it does not appear how the possession of two 

 ears helps us, though there is some evidence that it does ; and 

 even when sounds come to us from the right or left, the explana- 

 tion of the ready discrimination which is then possible with pure 

 tone is not so easy as might at first appear. We should be 

 inclined to think that the sound was heard much more loudly with 

 the ear that is turned towards than with the ear that is turned 

 from it, and that in this way the direction was recognized. But 

 if we try the experiment, we find that, at any rate with notes 

 near the middle of the musical scale, the difference of loudness 

 is by no means so very great. The wave-lengths of such notes 

 are long enough in relation to the dimensions of the head to forbid 

 the formation of anything like a sound-shadow in which the 

 averted ear might be sheltered. 



In concluding this imperfect survey of recent progress in physics, 

 I must warn you emphatically that much of great importance 

 has been passed over altogether. I should have liked to speak 

 to you of those far-reaching speculations, especially associated with 

 the name of Maxwell in which light is regarded as a disturbance 

 in an electro-magnetic medium. Indeed at one time I had 

 thought of taking the scientific work of Maxwell as the principal 

 theme of this address. But, like most men of genius, Maxwell 

 delighted in questions too obscure and difficult for hasty treat- 

 ment, and thus much of his work could hardly be considered upon 

 such an occasion as the present. His biography has recently 

 been published, and should be read by all who are interested in 

 science and in scientific men. His many-sided character, the 

 quaintness of his humor, the penetration of his intellect, his 

 simple but deep religious feeling, the affection between son and 

 father, the devotion of husband to wife, all combine to form a 

 rare and fascinating picture. To estimate rightly his influence 



