240 J. M. CATTELL made in a series, 5 being dropped in the corrected series. The numbers in Table VI. give the average from 10 series. Similar experiments were made in 1885, daylight and sound being used as stimuli. The averages given in Table VII, are as usual taken from 26 reactions. I put together the results of these experiments in Table VIII., the time when the attention was normal being taken as 0. TABLE VIII. I J C / Concen. Distr, Concen. Distr. Electric light 12 + 44 + 26 + 21 shock 5 + 25 3 + 34 Daylight 13 + 35
+ 13 Sound 23 + 31 - 10 + 20 A 13 + 34 + 3 + 22 It will be noticed that when the brain is otherwise occupied the reaction is lengthened, though not to a great extent. The time is however but little shorter when the subject makes a great exer- tion to react quickly than when he makes the reaction easily and naturally. These experiments support the hypothesis that a reaction is an automatic act, only needing the activities seated in the cortex to prepare its way. A noise did not in the case of B and C so disturb the subject as especially to interfere with the placing in readiness of the parts of the brain concerned in making the reaction. If the brain was busied by adding 17 after 17, it could not so well put the lower centres in readiness, and the time of the reaction was lengthened. On the other hand a great effort of the will could only slightly shorten the reaction by holding the path of communication and motor centre in a state of more un- stable equilibrium. There is still another way of distracting the attention. When the time of normal reactions was measured the stimulus came about a second after the signal (i.e., the starting of the chrono- scope), so the brain parts could be put in a state of complete readiness. It might be expected that we could not hold these parts very long in a state of unstable equilibrium, and experiments show this to be the case. Instead of always letting the stimulus occur from f to 1^ sec. after the signal, I let the maximum interval be about 2 sees., and obtained thb results given in Table IX. The averages show that the attention can be held strained, that is, the centres kept in a state of unstable equilibrium for 1 sec. B's time is slightly shorter than normal ; this is probably
