living image of the friend. But with the least distraction it vanishes like a soap bubble. In other cases the process is instantaneously 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 appears possessed of independent life, it seldom moves spontaneously, and its features reflect no play of thought; it also often disappears 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 sometimes, although very rarely, happens when I am tired and excited. I was trying to make one out, when I heard a crackling sound. Instantly the shadowy image was illumined by a brilliant 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 sensory intensity. Parish gives another good illustration. A physician, 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 its 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 statement here, as it would lead me too far astray into the field of normal 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.