820 THE POPULAR SCIENCE MONTHLY. 



number from one to the other, a third. Hunting-dogs show great 

 skill in threading mountain-paths and overcoming or avoiding ob- 

 structions, but no dog will remove a branch interposed in his way. 

 When the associations by which instinct works come into play 

 outside of or against their ordinary end, we may speak of their 

 working as imperfect, and may say that the animal is mistaken. 



We also have instincts that are characterized by the narrow- 

 ness of their end. Among them are the reflex actions. The eyes 

 wink when they are threatened with injury ; but they also wink 

 when a beneficial operation is performed upon them, to which the 

 winking is an obstacle, the action going on all the same when it is 

 useless or injurious. 



I believe it can be shown that this type of instinctive action is 

 also found in man, and that the origin of many types of errors 

 may be found in the application to particular cases, but excep- 

 tional, of what is generally right. This proposition is confirmed 

 by some errors of the senses. When a point on our retina is ex- 

 cited by an external pressure, we fancy we see something lumi- 

 nous in the ordinary field of vision of that point. Were it not for 

 the experience of previous observations of objects and their re- 

 flections, we should localize as things behind the glass the reflec- 

 tions which we see in mirrors. In this and most like cases, we are 

 acquainted with the mechanism of the phenomenon, and can dis- 

 tinguish between what is only the sensorial impression and what 

 we owe to memory. The separation vanishes in the higher regions 

 of psychic life. If we draw a line on a sheet of paper and cover 

 the end of it with another sheet, an observer not in the secret will 

 imagine it to be much longer than it is, because his conception is 

 based upon the fact that when one object lies upon another, it usu- 

 ally covers a considerable portion of it. We are subject to a con- 

 siderable number of illusions of this kind. The prestidigitator 

 takes advantage of one form of them when, by a quick look to 

 one side, he turns the eyes of the audience away from his manipu- 

 lation and gains an opportunity to execute the trick without de- 

 tection, although every one of his spectators had determined not 

 to lose sight of his hands. He is aware that a glance and particu- 

 lar adjustments of the head and eyebrows and lids will usually 

 suggest to the looker-on that he will see at a particular point 

 something more interesting than anywhere else within his field 

 of vision. At the same time the audience will not know why 

 they looked in that direction, and may not even be conscious of 

 having looked there. 



We thus deal on this domain, remote from the physiology of 

 the senses, with functions of the nervous system similar to what 

 we have seen in the hen and the winking. Thought follows its 

 course according to the usual process ; with more or less of con- 



