72 TEE POPULAR SCIENCE MONTHLY. 



of one another, on the same screen, and elicited a resultant face which 

 resembled no one of the components in particular, but included all. 

 Whatever was common to all the portraits became intensified by com- 

 bination ; whatever was peculiar to each portrait was relatively too 

 faint to atti'act attention, and virtually disappeared. I made a great 

 variety of experiments ; in some I optically superimposed images by 

 arrangements of lenses, mirrors, stereoscopes, or doubly refracting 

 crystals ; in others I combined separate photographic impressions upon 

 a single sensitized plate. The result was that I invariably found it 

 possible to make a generalized picture, having a remarkable appearance 

 of individuality, out of a collection of separate portraits, so long as the 

 latter bore a moderate resemblance to one another, and were taken 

 from the same point of view, and were of the same size. 



I argue that the mind of a man whose visualizing faculty is free in 

 its action forms these generalized images of its own accord out of its 

 past experiences. It readily reduces images to the same scale, through 

 its constant practice in watching objects as they approach or recede, 

 and consequently grow or diminish in size. It readily shifts images 

 to any desired point of the field of view, through its habit of follow- 

 ing bodies in motion to the right or left, upward or downward. It 

 selects images that present the same aspect, either by a simple act of 

 memory or by a feat of imagination that forces them into the desired 

 position, and it has little or no difficulty in reversing them from right 

 to left, as if seen in a looking-glass. In illustration of these general- 

 ized mental images let us recur to the boat, and suppose the speaker to 

 continue as follows : " The boat was a four-oared racing boat ; it was 

 passing quickly just in front of me, and the men were bending for- 

 ward to take a fresh stroke." Now, at this point of the story the lis- 

 tener ought to have a picture Avell before his eye. It ought to have 

 the distinctness of a real four-oar going either to the right or the left, 

 at the moment when many of its details still remained unheeded, such 

 as the dresses of the men and their individual features. It would be 

 the generic image of a four-oar formed by the combination into a 

 single picture of a great many sight-memories of those boats. 



In the highest minds a descriptive word is sufficient to evoke crowds 

 of shadowy associations, each striving to manifest itself. When they 

 differ so much from one another as to be unfit to combine into a single 

 idea, there will be a conflict between them, each being prevented by 

 the rest from obtaining sole possession of the field of consciousness. 

 There would, therefore, be no definite imagery so long as the aggregate 

 of all the pictures that the word could reasonably suggest, of objects 

 presenting similar aspects, reduced to the same size, and accurately 

 superposed, resulted in a mere blur ; but a picture would gradually 

 evolve as qualifications were added to the word, and it would attain to 

 the distinctness and vividness of a generic image long before the word 

 had been so restricted as to be individualized. If the intellect be slow, 



