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 NOTES ON "PREHENSION" IN IDIOTS. 79 propose to call this power Prehension from the analogy of Appre- hension and Comprehension, to both of which it is clearly related as a simpler process. It may be described as the mind's power of tdkimi on certain material ; in this case auditory sensations. Now, of course, this power of taking on need not necessarily go with that of taking in, but, on the other hand, we clearly cannot take in without first taking on, and the mental operation we have been testing thus seems a necessary preliminary to all obtaining of mental material, i.e., through auditory presentations. Under these circumstances w r e might expect that " span of pre- hension '' should be an important factor in determining mental grasp, and its determination one of the tests of mental capacity. The results given above, as far as they go, seem to confirm in no slight degree the theoretical probability. Supplementary Notes on " Prehension " in Idiots. By FRANCIS GALTON, F.K.S. Prof. Bain and myself paid a visit of 4J hours' duration to the Earls wood Asylum for Idiots, on June 18, 1886, where we were received by Dr. Cobbold, who gave us every assistance. There were 566 idiots in the asylum, and he picked out those who were the most suitable for our inquiries. He told us, and we had abundant evidence of the truth of the statement, that, as a general rule, idiots are incapable of the simplest arithmetic. Usually they cannot even add two figures together, though they may know the multiplication table by rote. On the other hand, a very few cases are to be met with in which idiots have a tenacious memory for dates. We determined to apply the test of the number of figures that can be orally repeated after having heard them read out once distinctly, to (1) the better class of idiots generally ; (2) those who had the special power of recollecting dates, and to test the latter in other ways as well. I. Nine of the best girls were selected by Dr. Cobbold out of the class-room. They could all read and write a little, and were intelligent enough to do some house work. They were aged apparently from 16 or 17 to 25. They all failed in adding two figures together, such as 3 to 5, 4 to 7, &c. Their performances in the numeral-test are given below at A. Six other girls were then taken by Dr. Cobbold from the same class not quite indiscriminately, as our wish at that moment was to find girls who were intelligent enough to answer quickly, and who were nevertheless unable to repeat many figures. The result was, however, that given at B.