NOMENCLATURE OF MENTAL OPERATIONS 109 



the bodily presentments of spiritual phenomena to 

 be, in the limbo of the brain. In that form of de- 

 sire which is called " attention," the train of 

 thought, held fast, for a time, in the desired direc- 

 tion, seems ever striving to get on to another line 

 and the junctions and sidings are so multitudinous! 



The constituents of trains of ideas may be 

 grouped in various ways. 



Hume says: 



" We find, by experience, that when any impression has 

 been present in the mind, it again makes its appearance 

 there as an idea, and this it may do in two different ways : 

 either when, on its new appearance, it retains a consider- 

 able degree of its first vivacity, and is somewhat inter- 

 mediate between an impression and an idea ; or when it en- 

 tirely loses its vivacity, and is a perfect idea. The faculty 

 by which we repeat our impressions in the first manner is 

 called the memory, and the other the imagination." (I. 

 pp. 23, 24.) 



And he considers that the only difference be- 

 tween ideas of imagination and those of memory, 

 except the superior vivacity of the latter, lies in the 

 fact that those of memory preserve the original 

 order of the impressions from which they are de- 

 rived, while the imagination " is free to transpose 

 and change its ideas." 



The latter statement of the difference between 

 memory and imagination is less open to cavil than 

 the former, though by no means unassailable. 



The special characteristic of a memory surely 

 is not its vividness; but that it is a complex idea, 



