THE PERCEPTION OF SPACE. 139 



In tlie skin itself there is a vague form of projection 

 into the third dimension to which Heriug has called atten- 

 tion. 



"Heat is not felt only against the cutaneous surface, but when com- 

 municated through the air may appear extending more or less out from 

 the surface into the third dimension of surrounding space. . . . We 

 can determine in the dark the place of a radiant body by moving the 

 hand to and fro, and attending to the fluctuation of our feeling of 

 warmth. The feeling itself, however, is not projected fully into the 

 spot at which we localize the hot body, but always remains in the 

 neighborhood of the hand." 



The interior of one's mouth-cavity feels larger when ex- 

 plored by the tongue than when looked at. The crater of a 

 newly-extracted tooth, and the movements of a loose tooth 

 in its socket, feel quite monstrous. A midge buzzing 

 against the drum of the ear will often seem as big as a but- 

 terfly. The spatial sensibility of the tympanic membrane 

 has hitherto been very little studied, though the subject 

 will well repay much trouble. If we approach it by intro- 

 ducing into the outer ear some small object like the tip of 

 a rolled-up tissue-paper lamplighter, we are surprised at 

 the large radiating sensation which its presence gives us, 

 and at the sense of clearness and openness wliich comes 

 when it is removed. It is immaterial to inquire whether 

 the far-reaching sensation here be due to actual irradiation 

 upon distant nerves or not. We are considering now, not 

 the objective causes of the spatial feeling, but its subjective 

 varieties, and the experiment shows that the same object 

 gives more of it to the inner than to the outer cuticle of 

 the ear. The pressure of the air in the tympanic cavity 

 upon the membrane gives an astonishingly large sensation. 

 We can increase the pressure by holding our nostrils and 

 closing our mouth and forcing air through our Eustachian 

 tubes by an expiratory effort ; and we can diminish it by 

 either inspiring or swallowing under the same conditions of 

 closed mouth and nose. In either case wc get a large round 

 tridimensional sensation inside of the head, which seems 

 as if it must come from the affection of an organ much 

 larger than the tympanic membrane, whose surface hardly 

 exceeds that of one's little-finger-nail. 



