n8 PSYCHO-PHYSICAL METHOD 



Fechner boldly set to work to devise methods by 

 which exact observations can be made, for he believed 

 that the proof he sought would-be yielded by an exact 

 determination of the quantitative relations of the physi- 

 cal to the psychical. In attempting this he naturally 

 turned to those states of consciousness which are most 

 clearly and immediately related to the physical world, 

 namely, the sensations. He sought to discover exact 

 quantitative relations between sensations and the physical 

 impressions, the stimuli to the sense-organs, by which 

 they are excited. 



That sensations have in some sense magnitude, 

 and differ from one another quantitatively, seems 

 clear. That an intense sensation, a bright colour- 

 sensation or a loud sound, is greater than a feeble 

 sensation, a faint colour or a feeble sound, seems indis- 

 putable ; but when we attempt to measure these magni- 

 tudes and to express them in numerical form we meet 

 with great difficulties. 



All physical measurement involves the comparison of 

 the quantity to be measured with some accepted standard 

 or sum of units of quantity. When, for example, we 

 measure a quantity of length or of weight, we find how 

 many times some conventional unit of length or of weight 

 is contained in the quantity to be measured, and we 

 express the quantity as a multiple of this unit. And in 

 physical measurement we can adopt various expedients 

 for reducing the equality or difference of the quantities 

 to be compared to some form easily and certainly appre- 

 hended by the senses. Thus, in measuring weight, we 

 are not content merely to compare the unknown quantity 

 directly with the known standard of weight ; but by 

 means of a balance we render the difference or equality 

 visible to the eye, which apprehends equality or 



