{m ) 



miglit be eniplovod, we nmst use for the iieui-a b, h c, c cl, d olc. 

 the expression 



:fir. 



— , ()3 == A' cIc 



T 1'. 



As the sliniiili i\., r.^, i\ etc. iire proporlioiial lo //, we iiiuy siih- 

 slitiite tbr tliese m^U, iii.Ji, rnjt etc. 



The (piestioii arises next: how shall we jisyehicallv coiiihiiie lliese 

 ini[)i'essi()iis in order to make use of Iheiti for the s|te('i;il |)iiri>ose 

 aimed at by our experiment, i. e. to decide whether two stimuli are 

 dilferent from one another? Summation oi' additioJi is out of tiie 

 (piestion : this wotdd be in contradiction Avith the experience (hat by 

 lixing oui' attention on a definite sensation, other sensations arc; 

 weakened. It is clear that we will conform our judgment to that part 

 of the sensation that is best fit for our purpose. Starting from tiiis 

 fact we may continue to treat the question mathematically. 



In the tirst place it ought to be taken \nU) consideration, that by 

 increment of a stimulus Jiot a small mind)er of new peripheral 

 neurones are stinudated, but generally a great many. In the case 

 of a pressure e.g. not only nerve-endings lying sideways of the 

 compressed surface, but also more profoundly situated end-organs 

 will be acted upon l)y increased intensity of stimidus. For every 

 indi\idual neui-on we shall luue U) put in anothei' coefficient ///. If 



iMg. L'. 



we construct lliei-efbre a ureat manv cui'xcs O,, o.,, o, all tiiese curves 

 will only be ditferent on account of liie constant /// being changed. 

 We now suppose the linal judgmeul fixed each lime by a pai't of 

 a farther situated curve. Thence it may be concluded, that the 



