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THE POPULAR SCIENCE MONTHLY. 



idea. One patient, witli abnormal skin-sensibility, believes he is 

 made of glass or stone ; another, for similar reasons, believes he 

 has an invisible persecutor constantly at his side. But for the 

 present we will assume that the judging powers do not vary be- 

 yond their normal limits. 



In every perception two factors contribute to the result. The 

 one is the nature of the object perceived, the other that of the 

 percipient. The effect of the first factor is well recognized, the 

 importance of the second factor is more apt to be overlooked. 

 The sunset is a different experience to the artist from what it is 

 to the farmer ; a piece of rocky scenery is viewed with quite dif- 

 ferent interests by the artist and the geologist. The things that 

 were attractive in childhood have lost their charm, and what was 

 then considered stupid, if noticed at all, has become a cherished 

 hobby. Even from day to day our interests change with our 

 moods, and our views of things brighten with the weather or the 

 good behavior of our digestive organs. Not only will the nature 

 of the impression change with the interests of the observer, but 

 even more, tvlietlier or not an object will be perceived at all will 

 depend upon the same cause. The naturalist sees what the stroller 

 entirely overlooks ; the sailor detects a ship in the distant horizon 

 where the landsman sees nothing; and this is not because the 

 naturalist and the sailor have keener vision, but because they 

 know what to look for. Whenever an impression is vague or an 

 observation made under poor conditions, this subjective element 

 comes to the front. The vague and changing outline of a cloud 

 is " almost in shape of a camel," or " like a weasel," or " like a 

 whale." Darkness, fear, any strong emotion, any difficulty in 

 perception show the same thing. " La nuit tons les chats sont 

 gris." Expectation, or expectant attention, is doubtless the most 

 influential of all such factors. When awaiting a friend, any indis- 

 tinct noise is readily converted into the rumbling 

 of carriage - wheels ; the mother hears in every 

 sound the cry of her sick child. After viewing an 

 object through a magnify ing-glass, we detect de- 

 tails with the naked eye which escaped our vision 

 before. When the answer in the book happens 

 to be wrong, nine tenths of the students will be 

 able to get it none the less. We can regard the 

 accompanying outline either as a book with the 

 back protruding toward us or receding from us. 

 Everywhere we perceive what we expect to per- 

 ceive, in the perception of which we have an interest. The process 

 that we term sensation, the evidence of the senses, is dual in char- 

 acter, and depends upon the eyes that see as well as upon the things 

 that are seen. 



