100 PSYCHOLOGY. 



showing that his idea of what metals as a class ought to be 

 had falsified the sensation he derived from a very light 

 substance. 



In the sense of hearing, similar mistakes abound. I 

 have already mentioned the hallucinatory effect of mental 

 images of very faint sounds, such as distant clock-strokes 

 (above, p. 71 ). But even when stronger sensations of sound 

 have been present, everyone must recall some experience 

 in which they have altered their acoustic character as soon 

 as the intellect referred them to a different source. The 

 other day a friend was sitting in my room, when the clock, 

 which has a rich low chime, began to strike. " Hollo ! " said 

 he, "hear that hand-organ in the garden," and was sur- 

 prised at finding the real source of the sound. I had myself 

 some years ago a very striking illusion of the sort. Sitting 

 reading late one night, I suddenly heard a most formidable 

 noise proceeding from the upper part of the house, which 

 it seemed to fill. It ceased, and in a moment renewed it- 

 self. I went into the hall to listen, but it came no more. 

 Resuming my seat in the room, however, there it was again, 

 low, mighty, alarming, like a rising flood or the avant- 

 coitrier of an awful gale. It came from all space. Quite 

 startled, I again went into the hall, but it had already 

 ceased once more. On returning a second time to the room, 

 I discovered that it was nothing but the breathing of a little 

 Scotch terrier which lay asleep on the floor. The note- 

 worthy thing is that as soon as I recognized what it was, I 

 was compelled to think it a different sound, and could not 

 then hear it as I had heard it a moment before. 



In the anecdotes given by Delbceuf and Reid, this was 

 probably also the case, though it is not so stated. Reid 

 says: 



" I remember that once lying abed, and having been put into a fright, 

 I heard my own heart beat; but I took it to be one knocking at the 

 door, and arose and opened the door oftener than once, before I dis- 

 covered that the sound was in my own breast." (Inquiry, chap. iv. 



§1.) 



Delboeuf s story is as follows : 



" The illustrious P. J. van Beneden, senior, was walking one evening 

 with a friend along a w^oody hill near Chaudfontaine. ' Don't you 



