ADDRESS. 21 



of the illumination is below the chromatic threshold — that is, too feeble 

 to awaken these activities — or when, as in the totally colour-blind, they 

 are wanting, it manifests itself independently ; all of which can be most 

 easily understood on such a hypothesis as has lately been suggested in 

 an ingenious paper by Mrs. Ladd Franklin, > that each of the elements of 

 the visual apparatus is made up of a central structure for the sensation 

 of light and darkness, with collateral appendages for the sensations of 

 colour — it being, of course, understood that this is a mere diagrammatic 

 representation, which serves no purposes beyond that of facilitating 

 the conception of the relation between the several ' specific energies.' 



EXPEEIMENTAL PSYCHOLOGY. 



Resisting the temptation to pursue this subject further, I will now ask 

 you to follow me into a region which, although closely connected with 

 the subjects we have been considering, is beset with greater difficulties — - 

 the subject in which, under the name of Physiological or Experimental 

 Psychology, physiologists and psychologists have of late years taken a 

 common interest — a borderland not between fact and fancy, but between 

 two methods of investigation of questions which are closely related, 

 which here, though they do not overlap, at least interdigitate. It is 

 manifest that, quite irrespectively of any foregone conclusion as to the 

 dependence of mind on processes of which the biologist is accustomed to 

 take cognizance, mind must be regarded as one of the ' specific energies ' 

 of the organism, and should on that ground be included in the subject- 

 matter of physiology. As, however, our science, like other sciences, is 

 limited not merely by its subject but also by its method, it actually takes 

 in only so much of psychology as is experimental. Thus sensation, 

 although it is psychological, and the investigation of its relation to the 

 special structures by which the mind keeps itself informed of what goes 

 on in the outside world, have always been considered to be in the physio- 

 logical sphere. And it is by anatomical researches relating to the 

 minute structure and to the development of the brain, by observation 

 of the facts of disease, and, above all, by physiological experiment, 

 that those changes in the ganglion cells of the brain and spinal cord 

 which are the immediate antecedents of every kind of bodily action have 

 been traced. Between the two — that is, between sensation and the 

 beginning of action — there is an intervening region which the physio- 

 logist has hitherto willingly resigned to psychology, feeling his incompe- 

 tence to use the only instrument by which it can be explored — that of 

 introspection. This consideration enables us to understand the course 

 which the new study (I will not claim for it the title of a new science, 

 regarding it as merely a part of the great science of life) has hitherto 



' Christine Ladd Franklin, ' Eine neue Theorie der Lichtempfindungen,' Zcitsclir. 

 fur Psychologie, vol. iv., 1893, p. 211 ; see also the Proceedings of the last Psycho- 

 logical Congress in London, 1892. 



