502 THE HUMAN BODY. 



right ear than the left; but on turning round the reverse is 

 the case; and half way round the loudness in each ear is the 

 same. Hence we are led, by mental laws outside of the 

 physiological domain, to suspect that its cause is not in our 

 Body, but outside of it; and depends not on a condition of 

 the Body but on something else And this is confirmed 

 when going in one direction we find the sound increased, 

 and in the other that it is diminished. This implies that we 

 have a knowledge of our movements, and this we gain 

 through the muscular sense. It constitutes the reactive side 

 of our sensory life, associated with the changes we produce 

 in external things; and is correlated and contrasted with the 

 passive side, in which other things produce sensations by act- 

 ing upon us. 



As regards our common sensations we find something of 

 the same kind. The more readily they can be modified by 

 movement the more definitely do we localize them in space, 

 though in this case within the Body instead of outside it. 

 Hunger and nausea can be altered by pressure on the pit of 

 the stomach; thirst by moistening the throat with water; 

 the desire for oxygen (respiration-hunger) by movements of 

 the chest; and so we more or less definitely ascribe these 

 sensations to conditions of those parts of the Body. Other 

 general sensations, as depression, anxiety, and so on, are not 

 modifiable by any particular movement, and so appear to us 

 rather as mental states, pure and simple, than bodily sensa- 

 tions. 



Sensory Illusions. " I must believe my own eyes " and 

 " we can't always believe our senses " are two expressions 

 frequently heard, and each expressing a truth. No doubt a 

 sensation in itself is an absolute incontrovertible fact: if I 

 feel redness or hotness I do feel it, and that is an end of the 

 matter: but if I go beyond^ the fact of my having a certain 

 sensation and conclude from it as to properties of something 

 else if I form a judgment from my sensation I may be 

 totally wrong; and in so far be unable to believe my eyes or 

 skin. Such judgments are almost inextricably woven up 

 with many of our sensations, and so closely that we cannot 

 readily separate the two; not even when we know that the 

 judgment is erroneous. 



For example, the moon when rising or setting appears 

 bigger than when high in the heavens we seem to feel 



