ii6 



SCIENCE. 



[Vol. XVI. No. 395 



be the most serious. It appears as a difHcolty in keeping 

 one's attention upon the experiment, and thus lengthens the 

 time, and especially the average variation of the experi- 

 ments. By fatigue is meant the fatigue brought about by 

 the experimenting itself. The time is also affected by gen- 

 eral fatigue preceding the experiment. Some individuals 

 are extremely sensitive to influences of this kind. 



(6) Individual Variations. The fact here to be investi- 

 gated is the general one that different persons require differ- 

 ent times for the performance of the same operations. The 

 difficulty of drilling a company of men to act in concert, 

 whether in military drill or otherwise, springs in part from 

 this difference. It was from this point of view, too, that 

 the time of mental processes was first studied. So long ago 

 as 1795 Maskelyne, the astronomer royal, discharged his as- 

 sistant because the latter recorded the transit of a star across 

 the wire of the telescope half a second or more later than he 

 himself. Some twenty-five years later Bessel, another as- 

 tronomer, had his attention called to the point, and upon in- 

 vestigation established the fact that no two observers re- 

 corded such transits at precisely the same time. The differ- 

 ence in time between any two observers was usually 

 expressed as an equation, and hence the term "personal 

 equation," which, though strictly applicable only to the 

 differences so found, has assumed a much wider meaning. 

 The individual differences become greater as the process to 

 be performed increases Ln complexity, and this explains in 

 part why the personal equations as determined by the com- 

 plicated eye and ear method were so large: with the simpler 

 method of electrical record these differences are much reduced. 

 Besides the differences due to practice and the mode of re- 

 action, there are a large number of minor sources of varia- 

 tion, which as yet are not suflBciently understood to justify 

 a correlation of quick or slow re-action tiuies with definite 

 individual qualities. We may, however, note (a) that the 

 time is longer in children than in adults, as has been shown, 

 amongst others, by Binet, who found that children from 3^ 

 to 7 years re-acted in from iAOff to 66(T, when adults required 

 but 140(7. In the very old the time is longer than in the 

 prime of life. Under the influence of mental or physical 

 fatigue, worry, or slight indisposition, the time has been in- 

 creased. Obersteiner, Vintschgau, Goldscheider, and others, 

 have incidentally observed these effects, showing an increase 

 of SOff to 4Qff. These variations are related to others, shad- 

 ing over into the abnormal. Under this head may be con- 

 sidered (7) the action of drugs and re-action times in the 

 insane. Several of the earlier experimenters made a few 

 observations concerning the effect of drugs. Exner found 

 quite a marked lengthening of the time after drinking wine. 

 Vintschgau and Dietl found that the effect of coffee was to 

 decrease and of morphium to increase the time for a consid- 

 erable period. The more elaborate researches of Eraepelin 

 show that the effect of amyl, ether, and chloroform is a 

 sudden lengthening of the re-action times, reaching a maxi- 

 mum in a very few minutes, and followed by a rather long 

 period of times slightly shorter than the normal. If a strong 

 dose of the drug be used the lengthening is more considera- 

 ble and the secondary shortening slighter. Thus Kraepelin, 

 whose normal re-action was ISSff, after a strong inhalation 

 of ether re-acted in SOSff, and in the period of shortening in 

 170(7; while with a light narcosis the maximum re-action 



was 223(7, and the shortened re-action 150(7. The effect of 

 alcohol, however, is a brief period of shortened times fol- 

 lowed by a long period of lengthened times. This is also 

 found by Orchansky, who, with a normal re-action of 155(7, 

 re-acts in 105(7 eight minutes after taking a dose of alcohol, 

 and in 225(7 after thirty minutes. The observations of War- 

 ren do not yield equally positive results, but do not conflict 

 with those of Kraepelin. Changes in the extent of the aver- 

 age variation have also been observed. On what psycho- 

 logical factors these differences depend it is difficult to say, 

 but the subjective feelings accompanying the lengthened 

 times are a difficulty in keeping the attentioQ upon the mat- 

 ter in hand, and an unwillingness to exert one's self. The 

 evidence afforded by the action of drugs upon these pro- 

 cesses is important as indicating the dependence of the 

 re-actions upon physiological conditions. A change of re- 

 action times in insanity has been frequently observed, but 

 the field for individual variation is here very large. It 

 seems probable that in most forms of mental disease, and 

 particularly in melancholia, there is a considerable length- 

 ening of the re-action time, amounting in extreme cases to 

 one-half or three-quarters of a second. In the excited forms 

 of disease, such as mania, a shortening has been observed. 

 Obersteiner cites a case of general paralysis in the incipient 

 stages of which the time was 166(7, in a more advanced 

 stage 281(7, in a most advanced stage 451c7. Stanley Hall 

 has found a marked shortening of the time in the hypnotic 

 condition, but his result is not corroborated by others. 

 Methods of Experimentation. 



The chief requisite in these experiments is an apparatus 

 for accurately measuring small intervals of time. The ear- 

 liest method, still in use, records the vibrations of a tuning- 

 fork upon the quickly-moving smoked surface of a rotating 

 drum, and beneath this the Qioment of giving the signal and 

 making the response. If a fork making one hundred vihra- 

 tions per second be used, whole hundredths can be directly 

 counted and smaller fractions estimated. Wundt has con- 

 structed a more accurate and specialized instrument in which 

 a fork making five hundred vibrations per second is used. 

 A very much simplified form of apparatus has been devised 

 by Obersteiner, in which the slide holding the record is 

 moved by hand, and the movement of re-action draws the 

 fork off the record; and by Bowditch, in which the fork it- 

 self carries the record, and the signal and re-action are indi- 

 cated by a shifting of the writing point. In the astronomical 

 records clockwork takes the place of a tuning-fork. The 

 objection to these methods is that they necessitate tedious 

 counting of curves. If the rate of the rotating-apparalus is 

 very uniform and frequently tested, one may substitute 

 measuring for counting, but the most convenient apparatus 

 for the purpose is the Hipp chronoscope. This instrument 

 contains a fine clock-work, set in motion by releasing a 

 spring and running for about half a minute. The hands of 

 the two dials, the one indicating tenths and the other thou- 

 sandths of a second, do not move until drawn away from a 

 set of cogs by the opening or closure of a magnetic circuit, 

 and are stopped again in the same way. By making the 

 usual arrangement whereby the production of the stimulus 

 sets the hands in motion and the re-acting movement brings 

 them to a stand-still, we can read off directly the interval of 

 the re-action time. Unless we can afford to sacrifice accu- 

 racy for convenience, a means of controlling the chrono- 

 scope is indispensable. This may be done by timing the fall 

 of a ball from a given height and comparing it with theo- 

 retical time. In the apparatus for this purpose supplied 

 with the chronoscope the ball is mechanically released, and 

 the mode of making the circuit is equally defective, so that 



