544 PSYCHOLOGY. 



Sounds are less delicately discriminated in intensity tiian 

 liglits. A certain difficulty lias come from disputes as to 

 the measurement of the objective intensity of the stimulus. 

 Earlier inquiries made the perceptible increase of the stim- 

 ulus to be about ^ of the latter. Merkel's latest results of 

 the method of just perceptible differences make it about 

 Y^^ for that part of the scale of intensities during which 

 Weber's law holds good, which is from 20 to 5000 of M.'s 

 arbitrary unit.* Below this the fractional increment must 

 be larger. Above it no measurements were made. 



For pressure and muscular sense we have rather divergent 

 results. Weber found by the method of just-perceptible 

 differences that persons could distinguish an increase of 

 weight of ^L when the tAvo weights were successively lifted 

 by the same hand. It took a much larger fraction to be 

 discerned when the weights were laid on a hand which 

 rested on the table. He seems to have verified his results 

 for only two pairs of differing weigiits,t and on this founded 

 his ' law.' Experiments in Bering's laboratory on lifting 

 11 weights, running from 250 to 2750 grams showed that 

 the least j)erceptible increment varied from ^\ for 250 grams 

 to yi^ for 2500. For 2750 it rose to -^^ again. Merkel's 

 recent and very careful experiments, in which the finger 

 pressed down the beam of a balance counterweighted 

 by from 25 to 8020 grams, showed that between 200 and 

 2000 grams a constant fractional increase of about yV was 

 felt when there was no movement of the finger, and of about 

 ji^ when there was movement. Above and below these 

 limits the discriminative poAver grew less. It was greater 

 when the pressure was upon one square millimeter of sur- 

 face than when it was upon seven.:}: 



Warmth and taste have been made the subject of similar 

 investigations with the result of verifying something like 

 Weber's law. The determination of the unit of stimu- 

 lus is, however, so hard here that I will give no figures. 

 The results may be found in Wundt's Physiologische Psy- 

 chologie, 3d Ed. i. 370-2. 



* Philosopliische Studien, v. 514-5. 



t Cf. G. E. Muller: Zur Grandlegung der Psychophysik, §§ 68-70. 



X Philosopbiscbe Studien, v. 287 £f. 



