THE GEOMETRICAL SENSE. 141 



But, it has been said, that touch is the least subject to error of all 

 the senses: it is the regulating the geometrical sense. In part only 

 is this accurate. It certainly possesses the advantage of allowing the 

 organ of sense to be brought into immediate contact with the body that 

 excites the impression ; whilst, in the case of olfaction, the organ receives 

 the impression of an emanation from the body; and, in vision and 

 audition, only the vibration of an intervening medium. Yet some of 

 the errors into which touch falls are as grievous as those that happen to 

 the other senses. How inaccurate is its appreciation of the temperature 

 of bodies ! We have attempted to show, that it affords merely relative 

 knowledge, the same substance appearing hot or cold to us, according 

 to the temperature of the substance previously touched. Nay, infalli- 

 bility so little exists, that we have the same sensation communicated by 

 a body that rapidly abstracts caloric from us, as by one that rapidly 

 supplies it. By touching frozen mercury, which requires a temperature 

 of 40 of Fahrenheit to be congealed, we experience the sensation of 

 a burn. Again, if we cross the fingers and touch a rounded body a 

 marble, for instance with two of the pulps at the same time ; instead of 

 experiencing the sensation of one body, we feel as if there were two, 

 an illusion produced by the lateral portions of fingers being brought 

 in apposition, which are naturally in a different situation, and at a 

 distance from each other; and, as these two parts habitually receive 

 distinct impressions when separated, they continue to do so when ap- 

 plied to opposite sides of the rounded body. 



It has been asserted, that the touch is the great corrector of the 

 errors into which the other senses fall. But let us inquire, whether, in 

 this respect, it possesses any decided superiority over them. For this 

 purpose, the distinction of the sensory functions into immediate and 

 mediate has been adopted. Each sense has its immediate function, which 

 it possesses exclusively ; and for which, no other can be substituted. The 

 touch instructs us regarding resistance; the taste appreciates savours; 

 the smell, odours ; audition, sound ; and vision, colours. These are the 

 immediate functions of the senses, each of which can be accomplished 

 by its own organs, but by no other. As concerns the immediate func- 

 tions of the senses, therefore, the touch can afford no correction. Its 

 predominance, as regards the mediate functions of the senses, is like- 

 wise exaggerated. The mediate functions are those that furnish im- 

 pressions to the mind; and by aid of which it acquires its notions of 

 bodies. The essential difference between these two sets of functions is, 

 that the mediate can be effected by several senses at once, and may be 

 regarded as belonging to the cerebrum. Vision, olfaction, and audition 

 participate in enabling us to judge of distances, as well as touch; the 

 sight instructs us regarding shape, &c. It has been affirmed by meta- 

 physicians, that touch is necessary to several of the senses to give them 

 their full power, and that we could form no notion of the size, shape, 

 and distance of bodies, unless instructed by this sense. The remarks 

 already made have proved the inaccuracy of this opinion. The farther 

 examination of it will be resumed under Vision. The senses are, in 

 truth, of mutual assistance. If the touch falls into error, as in the 



