632 POPULAR SCIENCE MONTHLY. 



living image of the friend. But with the least distraction it van- 

 ishes like a soap bubble. In other cases the process is instantane- 

 ously completed. Rev. Mr. F can at any time by an act of 



will create an image of a friend, and after doing so finds it hard 

 to lay the ghost which he has himself raised. Images voluntarily 

 externalized nearly always seem subject to curious limitations. 

 Often it is possible to externalize persons only, or only certain 

 persons, or only in definite attitudes. The apparition rarely ap- 

 pears possessed of independent life, it seldom moves spontaneous- 

 ly, and its features reflect no play of thought; it also often disap- 

 pears upon being touched. All these are common traits of ghosts, 

 and the identity goes to show their common origin. 



In the second place, the development of an idea is sometimes 

 clearly traceable to a simultaneous but disconnected sensory 

 stimulus. A striking illustration of this fact fell within my own 

 experience not long ago. I had had a fatiguing and anxious day, 

 and consequently could not sleep. As I lay in bed, dim, silhouette- 

 like forms began to outline themselves in the darkness, as some- 

 times, although very rarely, happens when I am tired and ex- 

 cited. I was trying to make one out, when I heard a crackling 

 sound. Instantly the shadowy image was illumined by a bril- 

 liant flash of white light, and I saw two dumb-bells lying crossed 

 with the balls toward me. For. a moment my impression was 

 that some one had brought a light into the room, although my 

 eyes were closed ; but upon opening them I found that my brother 

 had entered without a light through a Japanese screen made of 

 slender wooden rods strung lengthwise. The crackling sound 

 made by the parted screen had raised my thought-image to sen- 

 sory intensity. Parish gives another good illustration.* A i^hysi- 

 cian, while experimenting in this line, thought of a section of 

 liver and tried to see it, at the same time pressing on the ball 

 of the eye. " At first he was clearly conscious that his mental 

 image was quite dim and confused; yet suddenly an image of 

 a section of liver stood before his eyes as if seen through a 

 microscope, clearly outlined, and with all tts arteries, veins, 

 and gall ducts beautifully colored in red, blue, and greenish 

 violet.'' 



In the third place, the degree of vividness which a mental 

 state attains seems to bear an inverse relation to the number of 

 ideas which it suggests. I can not go into the proof of this state- 

 ment here, as it would lead me too far astray into the field of nor- 

 mal psychology, but those who care to follow it out will find it 

 set forth by Prof. James in his Psychology, volume ii, page 134. 

 It is also true that hallucinations are common in states in which 



* Ueber die Trugwahrnehmung, p. 134. 



'ii 



