THE SENSE OF FEELING. 273 



manner: The two points, when simultaneously applied to the skin, always pr* 

 duce a single sensation, not only when they touch one and the same circle of 

 sensation, but also when they touch two contiguous ones ; the larger the di- 

 ameter of the circles, so much the more considerable must be the distance in 

 order to reach beyond the boundaries of two neighboring circles, so that one, 

 perhaps several, circles which remain untouched shall be included between the 

 points of the compasses. When this latter case occurs, the double sensation, 

 the idea of locally separated impressions, seems to result from the circumstance 

 that the mind has within itself a consciousness of the intervening circles, be they 

 one or more, which remain untouched ; that in the ideal image of the cuticular 

 surface which is present to it, the mind, while it assigns a place to each of the 

 received impressions, perceives that there is a free space between the two which 

 is characterized by other local tokens. It is this consciousness of the situation 

 and number of the circles of sensation which also enables the mind to form an 

 estimate of the distance between the two points of the compasses, as soon as it 

 acquires a perception of their duality, an estimate, liowever, which, from ex- 

 amples before cited, we know to be subject to much error. We mentally esti- 

 mate the distance in question by the number of the circles of sensation lying 

 untouched between those to which the points are applied, and this appreciation 

 can have no absolutely correct value, because the unit of measure on which it 

 is founded, the diameter of a circle of sensation, is of very variable magnitude, 

 differing greatly in different parts of the cuticle. Place, for instance, the two 

 points of the compasses an inch apart, first on the skin of the cheek and then 

 on that of the finger, and if the same precautions be observed as were before stip- 

 ulated, the person subjected to the experiment will conceive the distance be- 

 tween the points to be considerably greater on the finger than on the cheek ; 

 because the circles of sensation of the finger are much smaller than those of the 

 cheek, Avhence in the former more of them lie untouched between the points 

 than in the latter. In this way also may be easily explained the illusion above 

 noticed of the seeming withdrawal of the points further from one another when, 

 preserving the same distance apart, they are gradually moved from the ear 

 towards the mouth ; the nearer we approach the latter the smaller become the 

 circles of sensation ; the greater the number of them which passes at the same 

 time between the jioiuts, the greater, therefore, seems to be the separation of 

 these points. 



It is impossible to measure the absolute magnitude of the circles of sensation 

 in different parts of the skin, because we do not know the number of those cir- 

 cles which, on the above theory, must remain untouched between the points of 

 the compasses in order that the sensation should be double. But their relative 

 magnitude we may measure with considerable accuracy, and thus determine the 

 comparative delicacy of the sense of place in different portions of the skin ; for 

 it is obvious that the degree of that sense assigned to any particular portion 

 must be so much the finer in proportion as the distance between the points of 

 the compasses can be reduced without a cessation of the divided sensation, or a 

 blending of the two simultaneous impressions into one. These measurements 

 have been executed with great care by the same eminent physiologist, C. H. 

 Weber, to whom the whole doctrine of the sense of touch is indebted for its 

 present form and clearness, as well as for the ingenious theory we have been 

 discussing. It has been ascertained that the sense of place is most delicate in 

 the end of the tongue, and next on the inner side of the last finger joints, the 

 points of the compasses requiring only a separation of i line in the former 

 case, and 1 line in the latter, to produce the double sensation. Much more ob- 

 tuse is the sense in the second finger joints, still more so in the palm of the 

 hand, and becoming duller and duller in other parts of the skin, it manifests, 

 18 s 



