THE UNCONSCIOUS ACTION OF THE BRAIN. 555 



continually used by her, and their form having become perfectly famil- 

 iar to her hands, would have been most readily recognized by her 

 sight ; and yet she did not know what they were ; she had not an idea 

 until she was told, and then she laughed, as she said, at her own stu- 

 pidity. No stupidity at all ; she had never learned it, and it was one 

 of those things which she could not know without learning. One of 

 the earliest cases of this kind was related by the celebrated Cheselden, 

 a surgeon of the early part of last century. Cheselden relates how a 

 youth just in this condition had been accustomed to play with a cat and 

 a dog ; but for some time after he attained his sight he never could tell 

 which was which, and used to be continually making mistakes. One 

 day being rather ashamed of himself for having called the cat the dog, 

 he took up the cat in his arms and looked at her very attentively for 

 some time, stroking her all the while ; and in this way he associated 

 the impression derived from the sight of the cat with the impression 

 derived from the touch, and made himself master (so to speak) of the 

 whole idea of the animal. He then put the cat down, saying, " Now, 

 puss, I shall know you another time." 



Now, the reason why I have specially directed your attention to 

 this is because it leads to one of the most important principles that I 

 desire to expound to you this evening what I call in Mental Physi- 

 ology the doctrine of resultants. All of you who have studied mechan- 

 ics know very well what a " resultant " means. You know that when 

 a body is acted on by two forces at the same time, one force carrying 

 it in this direction, and another force in that direction, we want to 

 know in what direction it will go, and how far it will go. To arrive 

 at this we simply complete what is called the parallelogram of forces. 

 In fact, it is just as if a body were acted on at two different times, by a 

 force driving it in one direction, and then by a force driving it in the 

 other direction. [Dr. Carpenter illustrated this point by the aid of 

 the black-board.] We draw two lines parallel to this, and we draw a 

 diagonal that diagonal is what is called the resultant ; that is, it ex- 

 presses the direction, and it expresses the distance the length of the 

 motion which that body will go when acted upon by these two forces. 

 Now, I use this term as a very convenient one to express this that 

 when we have once got the conception that is derived from the har- 

 monization of these two distinct sets of impressions on our nerves of 

 sense, we do not fall back on the original impressions, but we fall back 

 on the resultant, so to speak. The thing has been done for us ; it is 

 settled for us; we have got the resultant; and the combination giving 

 that resultant is that which governs the impression made upon our 

 minds by all similar and future operations of the same kind. We do 

 not need to go over the processes of judgment by which the two sets 

 of impressions are combined in every individual case ; but we fall back, 

 as it were, upon the resultant. Now, what is the case in the harmoni- 

 zation of the two classes of impressions of sight and touch, I believe to 



