476 STUDIES IN ADVANCED PHYSIOLOGY. 



Two voices do not sound twice as loud as one. The 

 experiment may be easily tried in a room where there are 

 several gas jets. After one jet has been lighted and the 

 intensity of the illumination of the room noted, it will take 

 a number of additional gas jets to make the room seem 

 doubly as light. 



CONFUSION OF SENSATIONS AND INFERENCES FROM 

 SENSATIONS. 



Many of our so-called special sensations are really not 

 sensations at all, but are inferences. To see the height of 

 a tree is an inference; to see the solidity of an object is an 

 inference; distance is wholly a matter of judgment, and the 

 perception of size a mere comparison. It, therefore, not 

 infrequently happens that our sensations mislead us. In 

 justice to the sensations, however, which in a normal body 

 probably never mislead but invariably tell the truth, it ought 

 to be said that it is not the sensations themselves which mis- 

 lead, but the inferences which we choose to draw from them. 

 In calling attention to these inferences it is not the purpose 

 here to carry the argument so far as to say with certain 

 philosophers that everything is an inference and nothing a 

 matter of knowledge ; that to see a certain color plainly 

 with the eye is not a trustworthy bit of knowledge, but a 

 mere inference drawn from a certain state of the body. 

 With this Cartesian philosophy physiology does not concern 

 itself, and the sensations which arise in the body normally 

 in every way are treated at once as trustworthy bits of 

 knowledge from which as premises true inferences may 

 logically be drawn. 



The special sense organs are discussed in the following 

 chapters in the order of their complexity, the simplest being 

 taken first. 



