178 PSYCHOLOGY. 



then along the whole of the hand iu question, we get a new 

 manner of measurement, less direct but confirming the 

 equivalencies established by the first. In these ways, by 

 superpositions of parts and by tracing lines on different 

 parts by identical movements, a person deprived of sight 

 can soon learn to reduce all the dimensions of his body to a 

 homogeneous scale. By applying the same methods to 

 objects of his own size or smaller, he can with equal ease 

 make himself acquainted with their extension stated in 

 terms derived from his own bulk, palms, feet, cubits, spans, 

 paces, fathoms (armspreads), etc. In these reductions it is 

 to be noticed that lohen the resident sensations of largeness 

 of two opposed surfaces conflict, one of the sensations is chosen 

 as the true standard and the other treated as illusory. Thus 

 an empty tooth -socket is believed to be really smaller than 

 the finger-tip which it will not admit, although it majfeel 

 larger ; and in general it may be said that the hand, as the 

 almost exclusive organ of palpation, gives its own magnitude 

 to the other parts, instead of having its size determined by 

 them. In general, it is, as Fechner says, the extent felt by 

 the more sensitive part to Avhich the other extents are re- 

 duced, * 



But even though exploration of one surface by another 

 were impossible, we could always measure our various 

 surfaces against each other by applying the same extended 

 object first to one and then to another. We should of 

 course have the alternative of supposing that the object 

 itself waxed and waned as it glided from one place to 

 another (cf. above, p. 141) ; but the principle of simplifying 

 as much as possible our world would soon drive us out of 

 that assumption into the easier one that objects as a rule 



* Fechner describes (Psychophysik, i. 132) a ' method of equivalents' 

 for measuring the sensibility of the skin. Two compasses arc used, one on 

 the part A, anotLier on the part B, of the surface The points on B must 

 be adjusted so that their distance apart appears equal to that between the 

 points on A With the place A constant, the second pair of points must be 

 varied a great deal for every change in the place B. though for the same A 

 and B the relation of the two compasses is remarkably constant, and con- 

 tinues unaltered for mouths pnjvided but few experiments are made on 

 each day. If, however, we practise daily liieir difference grows less, in 

 accordance with the law given in the text 



