THE UNCONSCIOUS ACTION OF THE BRAIN. 553 



the Sensory nerves, and of the motor nerves which answer to them, 

 grows up, as it were, in ourselves. We will take this illustration : Cer- 

 tain things are originally" instinctive, the tendency to them is born 

 with us ; but in a very large number of things we educate ourselves, 

 or we are educated. Take, for instance, the guidance of the class of 

 movements I was speaking of just now our movements of locomotion. 

 "We find that when we set off in the morning with the intention of 

 going to our place of employment, not only do our legs move without 

 our consciousness, if we are attending to something entirely different, 

 but we guide ourselves in our walk through the streets ; we do not run 

 up against anybody we meet ; we do not strike ourselves against the 

 lamp-posts ; and we take the appropriate turns which are habitual to 

 us. It has often happened to myself, and I dare say it has happened 

 to every one of you, that you have intended, to go somewhere else 

 that when you started you intended instead of going in the direct line 

 to which you were daily accustomed, to go a little out of your way to 

 perform some little commission; but you have got into a train of 

 thought and forgotten yourself, and you find that you are half-way 

 along your accustomed track before you become aware of it. Now, 

 there, you see, is the same automatic action of these sensory ganglia 

 we see, we hear for instance, we hear the rumbling of the carriages, 

 and we avoid them without thinking of it our muscles act in respond- 

 ence to these sights and sounds and yet all this is done without our 

 intentional direction they do it for us. Here again, then, we have 

 the " secondarily automatic " action of this power, that of a higher 

 nervous apparatus which has grown, so to speak, to the mode in which 

 it is habitually exercised. Now, that is a most important considera- 

 tion. It has grown to the mode in which it is habitually exercised ; 

 and that principle, as we shall see, we shall carry into the higher class 

 of Mental operations. 



But there is one particular kind of this action of the Sensory nerves 

 to which I would direct your attention, because it leads us to another 

 very important principle. You are all, I suppose, acquainted with 

 the action of the stereoscope; though you may not all know that 

 its peculiar action, the perception of solidity it conveys to us, depends 

 upon the combination of two dissimilar pictures the two dissimilar 

 pictures which we should receive by our two eyes of an object if it 

 were actually placed before us. If I hold up this jug, for instance, be- 

 fore my eyes, straight before the centre of my face, my two eyes re- 

 ceive pictures which are really dissimilar. If I made two drawings of 

 the jug, first as I see it with one eye, and then with the other, I should 

 represent this object differently. For instance, as seen with the right 

 eye, I see no space between the handle and the body of the jug; as I 

 see it with the left eye, I see a space there. If I were to make two 

 drawings of that jug as I now see it with my two eyes, and put them 

 into a stereoscope, they would bring out, even if only in outline, the 



