2 74 POPULAR SCIENCE MONTHLY. 



things than do the dogs and cats. Considering this and also their close 

 relationship physically to man, it seemed of special interest to discover 

 whether they could learn from example or from being put through 

 certain movements, whether they would manifest the capacity so evi- 

 dent in man and so lacking in the lower animals in general. 



I had one monkey for over a year and two others for about four 

 months. All three were of the genus Cebus. The general method of the 

 experiments was as follows : Boxes about a foot square were made with 

 small doors held by all sorts of contrivances. For instance, one was 

 held by a hook, another by a bar, another by a bolt, another by a wire 

 fastened firmly at one side and wound round a nail at the other. A bit 

 of food was put inside such a box and the door of the box left open. 

 The box was then put inside one of the large cages containing a monkey. 

 It would come down, reach into the box and get the food. After this 

 had been repeated a few times the box would be put into the cage, with 

 its door shut. The monkey would try to get in as before. He might 

 chance to operate the simple mechanism that held the door. If, how- 

 ever, he did not succeed of his own impulsive activity I would show 

 him or put him through the movement a few times and then leave him 

 to himself again to see if he had profited by the tuition. 



The general result was that they did not profit by the tuition, that 

 they did not gain and use ideas of how to open the doors, but learned 

 only by a process of selection from their own impulses. The meaning 

 and value of this general fact will aj^pear in the details of the experi- 

 ments. 



In order that such experiments shall be valid tests of the workings 

 of an animal's mind it is necessary that he surely desire to get into the 

 box, that he be not disturbed by the surroundings in any way that will 

 alter his mental efficiency, and that the experimenter be able to handle 

 him easily without frightening him or taking his attention away from 

 the box. In all cases it is further necessary to make sure that the 

 monkey sees you perform the acts you expect him to imitate, and sees 

 and feels himself make the movements you put him through. These 

 desiderata were obtained by testing the monkeys when hungry and 

 using bits of food of which they were especially fond as the attraction ; 

 by experimenting with them after they were quite used to their habitat 

 and to my presence ; by getting them into the habit of coming to me and 

 enjoying being handled, having their paws taken, etc.; by showing 

 them the act or putting them through it only when they were attend- 

 ing to the box. 



A sample of one of the experiments on the influence of example is 

 the following : The box used was arranged so that the door opened when 

 a brass lover was depressed about an eighth of an inch. The monkey 

 could reach this lever by putting his hand through a hole about an inch 



