320 PEHSONAL PREPAKATION FOR RESEARCH. 



observation belong to the subject of ' unconscious cerebra- 

 tion.' 



All our powers of observation are limited ; l and the 

 limits of their action depend both upon our inherited 

 and acquired ability. ' We can hear from 20 to 73,000 

 sonorous vibrations per second, or an extreme range of be- 

 tween 9 and 10 octaves. The cry of a bat is too acute 

 for some persons to hear ' 2 ; and a practised ear can dis- 

 tinguish 1209 from 1210 simultaneous vibrations per 

 second, of two tuning-forks. Professor Barrett has shown 

 that sounds which are inaudible to us may be detected 

 by means of a sensitive-flame. Various facts in natural 

 history render it probable that some animals, and espe- 

 cially insects, possess either senses which we do not, or 

 degrees of acuteness of sense exceeding ours. Izaac Taylor 

 (I think it was) remarked that if our minds were not de- 

 fended by the body from the influences of external nature 

 around us, our lives would be rendered miserable by the 

 acuteness of our sensations. It is not improbable that 

 by administering certain gases or vapours to ourselves, 

 and thus increasing the consciousness of a particular sense 

 whilst diminishing that of others, extremely feeble sounds, 

 odours, flavours, &c., might be detected which could not 

 otherwise be perceived. 



The power of observation is also liable to be interfered 

 with, diminished, or prevented, by various causes. Simul- 

 taneous observations of diverse phenomena can only rarely 

 be made; the observation of one thing, either by pre- 

 occupying the mind, or by exercising a more powerful 

 attraction upon it, usually prevents our simultaneously 

 observing another. Conflicting sensations are very effectual 

 in preventing observation, because they are a powerful 



1 See Chapter XXIV. 



2 Bain, Senses and Intellect, 2nd edit. p. 215. 



