232 OF SENSATION, AND THE ORGANS OF THE SENSES. 



within the netting that surrounds his bed, becomes a source of almost inexpres- 

 sible annoyance, when he is composing himself to sleep : and every one is 

 aware how vividly other sounds are perceived, when they break in upon the 

 stillness of the night, being increased in strength, not only by the contrast, 

 but by absorbing the whole attention. An interesting experiment is mentioned 

 by Miiller, which shows how completely the mind may be unconscious of im- 

 pressions communicated to it by one organ of sense, when occupied, even 

 without a distinct effort of the will, by those received through another. If we 

 look at a sheet of white paper through two differently-coloured glasses at the 

 same time, one being placed before each eye, the resulting sensation is sel- 

 dom that of a mixture of the colours ; if the experiment be tried with blue and 

 yellow glasses, for example, we do not see the paper of an uniform green, but 

 the blue is predominant at one moment, and the yellow at another, or blue 

 nebulous spots may present themselves on a yellow field, or yellow spots on a 

 blue field. We perceive, from this experiment, that the attention may not only 

 be directed to the impressions made on either retina, to the complete exclusion 

 of those of the other, but it may be directed to those made on particular spots 

 of either. This may be noticed, again, in the process by which we make 

 ourselves acquainted with a landscape or a picture ; if our attention be directed 

 to the whole field of vision at once, we see nothing distinctly ; and it is only 

 by abstracting ourselves from the contemplation of the greater" part of it, and 

 by directing our attention to smaller portions in succession, that we can obtain 

 a definite conception of the details. The same is the case in regard to audi- 

 tory impressions ; and here the power of attention in causing one sensation 

 or series of sensations to predominate over others, which are really more in- 

 tense, is often most remarkably manifested. When we are listening to a 

 piece of music played by a large orchestra, for example, we may either attend 

 to the combined effect of all the instruments, or we may single out any one 

 part in the harmony, and follow this through all its mazes ; and a person with 

 a practised ear (as it is commonly but erroneously termed, it being not the ear 

 but the mind that is practised), can even distinguish the sound of the weakest 

 instrument in the whole band, and can follow its strain through the whole 

 performance. This attention to a single element can only be given, however, 

 by withdrawing the mind from the perception of the rest ; and a musician 

 who thus listens, will have very little idea of the rest of the harmonic parts, or 

 of the general effect. In fact, when the mind is thus directed, by a strong 

 effort of the will, into a particular channel, it may be almost considered as un- 

 conscious quoad any other impressions. 



314. The effects of this principle are manifested in regard to the sensations 

 which originate within the system ; as well as in respect to those which are 

 excited by external impressions. Every one is aware how difficult it is to 

 keep the body perfectly quiescent,* especially when there is a particular 

 motive for doing so, and when the attention is strongly directed to the object. 

 This is experienced even whilst a Photogenic likeness is being taken, when 

 the position is chosen by the individual, and a support is adapted to assist 

 him in retaining it ; and it is still more strongly felt by the performers in the 

 Tableaux Vivans, who cannot keep up the effort for more than three or four 

 minutes. Now it is well known that, when the attention is strongly directed 

 to an entirely different object, (when we are listening, for example, to an elo- 

 quent sermon, or an interesting lecture,) the body may remain perfectly 

 motionless for a much longer period; the uneasy sensations which would 

 otherwise have occasioned the individual to change his position, not being felt : 

 but no sooner is the discourse ended than a simultaneous movement of the 



* Of course the movements of respiration and winking are left out of the question. 



