76 Dr Graves oil the Sense of Touch, 



taining it. Weber has ascertained that in most men, the left 

 side of the body and the left extremities enjoy a more accurate 

 perception of weight than the right, so far as weiglit is estimated 

 by pressure ; of fourteen different persons experimented on, the 

 left side of the body and the left extremities were found to be 

 more sensible of weight, measured by pressure, than the right, in 

 eleven ; in two the contrary was observed, and in one only no 

 difference between the sides could be detected. He offers no sa- 

 tisfactory explanation of this very remarkable and hitherto un- 

 observed phenomenon, which is obviously of some value as mak- 

 ing an original difference between the nervous power of the right 

 extremities and right side of the trunk, as compared with the left, 

 a difference which favours the idea, now indeed generally admit- 

 ted, that we cannot explain the circumstance of man being right- 

 handed and right-footed, except on the hypothesis of an original 

 difference in the vital powers of the right and left halves of the body. 



Weber next proceeds to make some observations, De Subti- 

 litate T actus in sentiendo colore. 



I long ago maintained the opinion, that the perception of heat 

 and cold is not a mere modification of the sense of touch. I am 

 glad to find this view of the subject advocated by so high an au- 

 thority as Lord Brougham, who, in his Discourse on Natural 

 Theology, p. 3, note, remarks, that " there seems as little reason 

 for arranging the sense of heat and cold under touch, as for ar- 

 ranging sight, smell, hearing, and taste, under the same head."" 

 Experiments made for the purpose of comparing the energy of 

 this sense in different parts of the body, are attended with ob- 

 vious difficulties ; thus if the surface of the substance applied to 

 the body be not exactly of the same extent in two cases, the re- 

 sult is not to be relied on, for, cateris paribus, a larger body 

 will feel hotter or colder than a smaller, and that in a very re- 

 markable degree. Thus, let one vessel contain water heated to 

 98°, and another water at 104° ; now if the finger be placed in 

 the latter, and the whole of the other hand be immersed in the 

 cooler, we shall be led to form a wrong judgment, and will pro- 

 nounce the water at 98° to be hotter than that at 104° ! In 

 some cases the same error was made when the difference of tem- 

 perature amounted to eight degrees, the hotter being at 106°. If 

 the parts were kept a good while immersed, the person some- 

 times becomes sensible of his error, and judges rightly. 



