66 THE POPULAR SCIENCE MONTHLY. 



end of a sitting all the numbers on which, he has been set to work, 

 in the different questions put to him. This experiment, which I 

 saw made at the Salpetriere, gives really incredible results. A 

 large number of problems were given to M. Inaudi during the 

 afternoon, the data of all of which were preserved in writing, in 

 order to verify the exactness of the repetition. On this day he 

 repeated two hundred and forty-two problems. It is said that he 

 repeated four hundred at a sitting given in the Sorbonne. 



These numbers, however, should not be taken as the measure 

 of M. Inaudi's memory for figures, because he did not learn them 

 one after another, without interruption. They were contained in 

 distinct experiments, in which the calculator burdened his mem- 

 ory each time with only twenty-four figures. He therefore had 

 intervals of rest, however brief ; and these rests probably facili- 

 tated the assimilation of the whole mass, which was really enor- 

 mous. Usually, he told us, he did not try to retain groups of 

 more than twenty-four figures. One day, twenty-seven were given 

 out to him. That was the maximum number that was essayed. 

 I proposed to him to recite twenty-six, and he was able to repeat 

 them all exactly by employing his usual processes. The experi- 

 ment tired him a little. After a short rest, I read fifty-two fig- 

 ures to him. In the middle of the experiment, when he had 

 reached the twenty-sixth figure, I pronouncing them and he 

 repeating them, he stopped. He was troubled, and expressed a 

 fear that he would forget the whole. He then repeated rapidly 

 from memory the figures which had just been pronounced, after 

 which he asked me to continue. I went on then to fifty-two 

 figures. He then tried to repeat them all. He did it, but with 

 some transpositions and confusions, and about ten mistakes. The 

 number fifty-two seems to constitute a limit for him. 



We have now to examine a little more closely what is meant 

 by the memory for figures ; for there are an immense variety of 

 psychological types, and the same mental operation may be com- 

 prehended and performed by two persons under absolutely dif- 

 ferent forms. There are many ways of fixing figures in the 

 memory and calling them out again ; or, in other words, several 

 images of a different kind are employed. According to the in- 

 vestigations of the committee of the Academy, M. Inaudi's pro- 

 cesses are the contrary of those which arithmetical prodigies are 

 generally supposed to use. 



These persons, according to their own testimony, are accus- 

 tomed to take visual memory as the basis of their mental opera- 

 tions. They have an inner vision of the numbers that are pro- 

 nounced, and those numbers, during the whole time of the 

 operation, stand before their imaginations as if they were written 

 on a tablet set before their eyes. This process of visualization 



