534 THE POPULAR SCIENCE MONTHLY. 



sions are of necessity fertile sources of superstition and fallacy from 

 which the child and the savage are never free, and with which all 

 branches of knowledge are largely tainted in their prescientific stage. 

 Lastly, that it is only by the strict methods of scientific inquiry, namely, 

 by measurement and number, that these fallacies can be cleared away 

 and the truth discovered. 



The physiological aspect of simple and blended memories is in- 

 telligible enough in its broad outlines, and may be briefly described. 

 Whenever any group of brain elements has been excited through an 

 impression of one of the senses, it becomes, so to speak, tender and 

 liable to become again excited, under the influence of other kinds of 

 stimuli. Whatever may be the cause of any new excitation, the result 

 of its reproduction is to create an imaginary sense-impression, similar 

 to that by which the first excitation had been caused ; and this we call 

 memory. Blended memories must necessarily follow the excitation of 

 many associated groups of brain elements, under the influence of a 

 stimulus that sets them simultaneously in action. 



Faint memories are particularly apt to blend together, and they 

 often defy analysis afterward. We are shown some picture of moun- 

 tain and lake, from a county we have never visited, yet it seems famil- 

 iar to us ; it accords with what we have seen dozens of times in Scot- 

 land or Switzerland or elsewhere, but our memories are confused and 

 obscure, and we can not wholly disentangle the incidents to which 

 they relate. 



Memories that are extremely vivid may at the same time be very 

 mobile, and capable of blending together. Much instruction on these 

 matters can be derived from those who possess the power of what is 

 called the visualizing faculty, in a high degree. The objects of their 

 memory are conspicuous images ; they can retain them for a long time 

 before the eye of their mind, they can dismiss or change them at will, 

 and they can, if they please, subject them to careful examination from 

 every side. I do not know any faculty that varies so much as this in 

 different persons. None can vary more, because its range lies between 

 perfection and nothingness. It is sometimes absolutely deficient, for 

 there are persons who never see mental images even in dreams, and 

 there are others who are said to have lost the power of seeing them. I 

 need not speak of cases where the visualizing power is feeble, as they 

 are common. Many are like those to whom St. James alludes when 

 he speaks of " a man beholding his natural face in a glass, who behold- 

 eth himself and goeth his way, and straightway forgetteth what man- 

 ner of man he was." It will be more to my point to show how perfect 

 the visualizing faculty sometimes is, at the same time that the images 

 may be moved with the utmost facility in the field of the mind's eye, 

 which is a first step toward their blending together. Out of the many 

 available instances I will only quote one, and will choose that one 

 chiefly because it has recently excited some public attention. There 



