CHAP. vi.J SOME OTHER SENSATIONS. 305 



phantoms. Compared with visual sensations however our tactile 

 sensations are so to speak fragmentary. A momentary exposure 

 of the retina may fill the mind with a complex visual image, 

 full of the most varied incident ; but the tactile impressions 

 which we can receive at any one moment are lew and simple. 

 Hence our tactile phantoms are also simple ; we may fancy that 

 some invisible garment has swept past us, or that a scorching 

 flame has passed near us, we may feel that the hand or that the 

 head is swollen and large, and we may experience an imaginary 

 pain in every region of the skin in turn ; but the most that we 

 can thus feel is simple compared with the possible complexity of 

 an ocular or even an auditory phantom. 



898. Like other sensations our tactile sensations while they 

 sometimes give us trustworthy information of the external world 

 at other times may give rise to illusions. This is well illustrated 

 by the so-called experiment of Aristotle. It is impossible in an 

 ordinary position of the fingers to bring the radial side of the 

 middle finger and the ulnar side of the ring finger to bear at the 

 same tims on a small object such as a marble. Hence when with 

 the eyes shut we cross one finger over the other, and place a 

 marble between them so that it touches the radial side of the one 

 and the ulnar side of the other, we recognize that the object is 

 such as could not under ordinary conditions be touched at the 

 same time by these two portions of our skin, and therefore judge 

 that we are touching not one but two marbles. Upon repetition 

 however we are able to correct our judgment and the illusion 

 disappears. 



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