610 rSYCUOLOGY. 



correctly noticed by him ;it the time. The average waa 

 here 0.18-iU". Hall and Jastrow listened to the intervals 

 between the clicks of their apparatus. Between two such 

 equal intei'vals of 4.27" each, a middle interval was includ- 

 ed, Avhich might be made either shorter or longer than the 

 extremes. 'After the series had been heard two or even 

 three times, no impression of the relative length of the 

 middle interval would often exist, and onl}' after hearing 

 the fourth and last [repetition of the series] would the 

 judgment incline to the plus or minus side. Inserting the 

 variable between two invariable and like intervals greatly 

 facilitated judgment, which between two unlike terms is far 

 less accurate." * Three observers in these experiments 

 made no error when the middle interval varied ^L- from the 

 extremes. When it varied -j^-^, errors occurred, but were 

 few. This would make the minimum absolute difference 

 perceived as large as 0.355." 



This minimum absolute difference, of course, increases 

 as the times compared grow long. Attempts have been 

 made to ascertain v/hat ratio it bears to the times them- 

 selves. According to Fechner's * Psychophysic Law ' it 

 ought always to bear the same ratio. Various observers, 

 however, have found this not to be the case.f On the con- 

 trary, very interesting oscillations in the accuracy of judg- 

 ment and in the direction of the error — oscillations depen- 

 dent upon the absolute amount of the times compared — 

 have been noticed by all who have experimented with the 

 question. Of these a brief account may be given. 



In the first place, in every list of internals experimented 

 ivith there will be found ivhat Vierordt calls an 'indifference- 

 point;' that is to say, an interval which we judge with max- 

 imum accuracy, a time which we tend to estimate as neither 

 longer or shorter than it really is, and away from which, 



* Mind, XI. 61 (1886). 



f Mach, Wiener Sitzungsb., Li. 2. 133 (1805); Estel, loc. cit. p 65, 

 Mehncr, loc. cit. p. 580, Buccola, op. cit. p. 378. Fechner labors to prove 

 that his law is only overlaid by other interfering laws in the figures re 

 corded by these experimenters; but his case seems to me to be one of des. 

 perate infatuation with a hobby. (See Wundt's Philosophische Studien 

 m. 1 ) 



