TRANSACTIONS OF THE SECTIONS. 139 



■will sliow that it is almost impossible to ascertain the effect of a stimulus upon a 

 retina which has never before been affected. This difficulty has been felt by all 

 experimenters. Molecular action in such a structure has been in operation from 

 the very beginning:, and such action, if of sufficient intensity, must produce a cer- 

 tain effect on the conducting-tract and on the recipient centre. This effect, although 

 of too weak mtensity to produce those clianges which residt in consciousness, must 

 be taken into account in the measurement of the intensity and duration of sensory 

 impressions. Thus the eye has a light of its own due to changes in the retina, 

 although this may ne^■er be conscious to us as a luminous impression. This con 

 ception of the state of matters in a terminal organ such as the retina, when applied 

 to actions going on in the brain, at once indicates that similar actions, or rather 

 that similar states of unrest, of change, variation, and moditication, are going on in 

 tliese deeper parts whicli may ne^er result in consciousness, per se, but which alto- 

 gether may have an inHuence on our mental existence comparable to that of tlie 

 feeble impressions constantly transmitted to the cerebrum from the viscera, some- 

 times termed the internal senses. 



Relation between Strength of Sensation and Magnitude op 



Stimulus. 



Having sho-s^ii that sensory impressions are distinctly related to time, the next 

 advance made by physiologists was to prove that there was a relation between the 

 .strength of the sensation and the magnitude of the stimulus, Here there are 

 difficulties in explaining what is meant, because language fails. We have no words 

 to discriminate ideas which hitherto have related to two distinct fields of know- 

 ledge — the objective and the subjecti-\-e. To speak of the strength or magnitude 

 of a sensation seems to be using terms applicable only in another region, .and quite 

 inapplicable to psychological phenomena, although no one has any doubt in distin- 

 guishing the intensity or magnitude of one pain from that of another. There is no 

 difficulty in understanding the phrase-magnitude of the stimulus. A weight often 

 pounds is greater than that of one pound, light from ten candles of equal size is more 

 than that given out by one, and the tones of a ■\iolin of equal pitch and quality 

 may vary in intensity according to the pressure of the bow on the string. It is 

 difficult, however, to obtain an absolute measurement of variations m sensation, 

 which is, of course, a subjective phenomenon. This can onlj'^ be done by varying 

 the objective cause, by observing a large number of instances, and by expressing 

 variations in the subjecti\-e phenomenon in terms applied to -(-ariations in the ob- 

 jective cause. If the average result obtained from a large number of instances 

 indicates any ratio between the magnitude of the stimulus and the subjective phe- 

 nomenon, then we may conclude that there is a relation between the two. 



This mode of inquiry, first originated by Professor E. II. AVeber, m his cele- 

 brated experiments on tactile impressions (and which were first introduced to 

 notice in this coimtry by Professor AUen Thomson), was afterwards earned out by 

 his colleague Professor Fechner, and has been subsequently elaborated by Professor 

 Wundt. It has led to various remarkable results, the chief of which are (1) 

 that in the case of each sense there is an upper and a lower limit, beyond which 

 the amoiuit of stimulus produces no appreciable difference of effect ; and (2) that 

 within this range there is a definite ratio between the stimulus and the amoimt of 

 the sensation. The upper limit beyond which an increase of external stimulation 

 is not followed by any observable increase in sensational effect was first obsened 

 by Professor Wundt. The lower hmit has been noted by many observers, and it is 

 indicated in almost every physiological text-book. Now^ it does not matter much 

 to us, in taking a general view- of things, v>hat the hmits are, provided we are sure 

 thfit such limits exist, inasmuch as it indicates another element of proof that psycho- 

 logical plienomena, so far as seufation is concerned, occur within certain physical 

 limits. 



FeCHNEBS iNVESTIfiATIONS. 



The next step naturally was to establish the ratio between the magnitude of the 

 stimulus and the magnitude of the sensation. To do this directly is impossible, as 



