ADDRESS. 1 9 



proceeds, but by what steps we attain that end has not yet been satis- 

 factorily 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 instinctive. 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 explanation of the 

 ready discrimination which is then possible with pure tones, 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 recognised. 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 lono- 

 enough in relation to the dimensions of the head to forbid the forma- 

 tion 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 

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

 such an occasion as the present. His biography has recently been pub- 

 lished, and should be read by all who are interested in science and in 

 scientific men. His many-sided character, the quaintness of his humour 

 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 upon the present state of science, we must regard 

 not only the work that he executed himself, important as that was, 

 but also the ideas and the spirit which he communicated to others. 

 Speaking for myself as one who in a special sense entered into his 

 labours, I should find it difficult to express adequately my feeling of 

 obligation. The impress of his thoughts may be recognised in much of 

 the best work of the present time. As a teacher and examiner he was 

 well acquainted with the almost universal tendency of uninstructed minds 



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