616 PSYCHOLOGY. 



part, we contract a habit of leaving it unnoticed, and at last 

 grow callous to its presence. Helmlioltz was the first psy- 

 chologist who dwelt on these facts as emphatically as they 

 deserve, and I can do no better than quote his very words. 



"We are accustomed," he says, *" in a large number of cases where 

 sensations of different kinds, or in different parts of tlie body, exist 

 simultaneously, to recognize that they are distinct as soon as they are 

 perceived, and to direct our attention at will to any one of them sepa- 

 rately. Thus at any moment we can be separately conscious of what 

 we see, of what we hear, of what we feel ; and distinguish what we feel 

 in a finger or in the great toe, whether pressure, gentle touch, or 

 warmth. So also in the field of vision. Indeed, as I shall endeavor to 

 show in what follows, we readily distinguish our sensations from one 

 another wfien we have a precise knowledge that they are composite, as, 

 for example, when we have become certain, by frequently repeated and 

 invariable experience, that our present sensation arises from the simul- 

 taneous action of many independent stimuli, each of which usually ex- 

 cites an equally well-known individual sensation." 



This, it will be observed, is only another statement of our 

 law, that the only individual components which we can 

 pick out of compounds are those of which we have inde- 

 pendent knowledge in a separate form. 



"This induces us to think that nothing can be easier, when a num- 

 ber of different sensations are simultaneously excited, than to distin- 

 guish them individually from each other, and that this is an innate 

 faculty of our minds. 



"Thus we find, among other things, that it is quite a matter of 

 course to hear separately the different musical tones which come to our 

 senses collectively; and we expect that in every case when two of them 

 occur together, we shall be able to do the like. 



" The matter becomes very different when we set to workto investi- 

 gate the more unusual cases of perception, and seek more completely to 

 understand the conditions under which the above-mentioned distinction. 

 can or cannot be made, as is the case in the physiology of the senses. 

 We then become aware that two different kinds or grades must he dis- 

 tinguished in our becoming conscious of a sensation. The lower grade 

 of this consciousness is that in which the influence of the sensation in 

 question makes itself felt only in the conceptions we form of external 

 things and processes, and assists in determining them. This can take 

 place without our needing, or indeed being able, to ascertain to what 

 particular part of our sensations we owe this or that circumstance in 

 our perceptions. In this case we will say that the impression of the 

 sensation in question is perceived synthetically. The second higher 

 grade is when we immediately distinguisli the sensation in question a? 



