number that he can repeat without mistake. Such trials are common in psychological laboratories. According to my personal observations, persons can repeat on an average from seven to ten figures without making a mistake, when they are pronounced with a rapidity of two per second. The division of figures into groups, the special vocal intonation, or some kind of rhythm, are artifices which may sometimes increase the number, and make the effort to repeat less painful. These results agree with those of an American psychologist, Mr. Jastrow, who mentions 8.5 as the average number found among pupils in his country.
M. Inaudi has practiced this kind of repetition for a long time. We repeat the number, dividing it into periods of three figures each, and giving the value of each period. For example, to make him repeat the number 395,820,152,873,642,586, we give it out, three hundred and ninety-five quadrillions, eight hundred and twenty trillions, one hundred and fifty-two billions, eight hundred and seventy-three millions, six hundred and forty-two thousand, five hundred and eighty-six. We are careful to dwell on the articulation of the numbers. M. Inaudi repeats, as fast as he comprehends it, each period of three figures; then, when he has taken in the complete number, he says confidently, "I know it," and repeats the whole series with great volubility.
I have witnessed his repetition in this way, without mistake, of a series of twenty-four figures. M. Charcot, in order to compare his capacity with that of Mondeux, another famous calculator, repeated with him the experiment, which had been tried with Mondeux, of telling off a number of twenty-four figures, divided into four periods, so that he might announce at will the six figures included in each of the periods. Mondeux took six minutes to reach the result; M. Inaudi only had to hear the figures given out. Thus a single hearing suffices M. Inaudi to fix in his mind a long series of figures or the statement of a complicated problem; he does not go back to repeat the numbers several times as we are obliged to do. He only asks, when the series of figures is a little long, to have it pronounced slowly. Once fixed in his memory, the number is retained with a precision and sureness which it is hard to conceive. M. Inaudi can not only repeat a number of twenty-four figures in the order in which he heard it, but in an inverse order, beginning with the units; he can repeat half the number in one direction, and the other half in the other direction; and all this without hesitation, without fatigue, and without mistakes.
Ordinary persons can recollect a number of many figures only a few seconds unless they have aids to their memory. M. Inaudi's memory retains for a very long time the numbers that have been given to him. He is in the habit of repeating at the
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