ATTENTION. 



413 



true laws to appear. Although my own experiments extend over manj 

 years (with interruptions), they are not even yet numerous enough to ex- 

 haust the subject — still, they bring out the principal laws which the 

 attention follows under such conditions." * 



Wundt accordingly distinguishes the direction ir ova the 

 amoimt of the apparent displacement in time of the bell- 

 stroke. The direction depends on the rapidity of the 

 movement of the index and (consequently) on that of the 

 succession of the bell-strokes. The moment at which the 

 bell struck was estimated by him with the least tendency 

 to error, when the revolutions took place once in a second. 

 Faster than this, positive errors began to prevail ; slower, 

 negative ones almost always w-ere present. On the other 

 hand, if the rapidity went quickening, errors became nega- 

 tive ; if slowing, positive. The amount of error is, in gen- 

 eral, the greater the slower the speed and its alterations. 

 Finally, individual differences jDrevail, as well as differences 

 in the same individual at different times.f 



* Physiol. Psych., 2d ed. ii. 264-6. 



f This was the original 'personal equation ' observation of Bessel. An 

 observer looked through his equatorial telescope to note the moment at 

 which a star crossed the meridian, the latter being marked in the telescopic 

 field of view by a visible thread, beside which other equidistant threads 

 appear. " Before the star reached the thread he looked at the clock, and 

 then, with eye at telescope, counted the seconds by the beat of the pendu- 



a 



^^ 



■^<r 



Fig iS. 



lum. Since the star seldom passed the meridian at the exact moment of a 

 beat, the observer, in order to estimate fractions, had to note its position 

 at the stroke before and at the stroke after the passage, and to divide the 

 time as the meridian-line seemed to divide the space. If, e.g., one had 



