WEBER'S LAW 457 



ferent parts of the drawing produced proportionally different .variations in 

 the resulting sensations. It is owing to this same peculiarity of our organ 

 of vision that we do not see the stars in daylight. The amount of light which 

 the stars contribute to the illumination of the heavens is too slight in propor- 

 tion to the total illumination for us to detect them. 



Merkel has shown that the same law holds for the sense of hearing, and 

 Camerer and Kepler for the sense of taste. 



Weber's law is true within fairly wide limits for all the senses, but for 

 very high or very low degrees of intensity certain variations come in. How- 

 ever, since the stimuli of medium intensity are the ones that occur most com- 

 monly in our everyday life, we may say that in general our estimates of 

 differences in intensity follow this law. 



In attempting a theoretical explanation of Weber's law it must not be for- 

 gotten that the conscious sensation aroused by an external stimulus occurs only 

 when the excitation begun at the sense organ reaches the cerebral cortex. It is 

 possible that in the purely physiological events taking place in the peripheral 

 sense organ, in the nerves and in the central nervous system a certain increase 

 in the stimulus produces the same absolute increase in the excitation aroused. 

 If so, the relationship expressed in Weber's law would be due to something which 

 is peculiar to the process of arousing a conscious sensation from a physiological 

 excitation. But it is also conceivable that the peripheral sense organ, nerves, 

 etc., themselves react in accordance with Weber's law, and that the law is there- 

 fore a purely physiological one. The latter alternative is probably correct, for 

 approximately the same relationship of excitation to intensity of stimulus has 

 been observed in many purely physiological processes. 1 



REFERENCES. W. James, "Principles of Psychology," New York, 1905. 

 0. Kulpe, " Outlines of Psychology," translated by E. B. Titchner, New York 

 and London, 1901. 



1 Fechner sought to deduce from this law of Weber a more general one. known as the 

 psychophysical law. By giving the former an algebraic expression and using the dif- 

 ferential calculus he arrives at the formula E=C log. nat. r. (where E is the sensation, C a 

 constant, and r the stimulus), which means that the sensation is proportional to the natural 

 logarithm of the stimulus. So many objections have been urged against this formulation 

 that its further consideration here seems unwarranted by its importance for the physiolog- 

 ical side of the questions involved. ED. 



