THE ART OF SCIENTIFIC INVESTIGATION 



leap on the man, and there have been serious protests that natives 

 were sacrificed to make such a film. Another illustration of the 

 subjective error is provided by the following anecdote. A 

 Manchester physician, while teaching a ward class of students, 

 took a sample of diabetic urine and dipped a finger in it to taste 

 it. He then asked all the students to repeat his action. This they 

 reluctantly did, making grimaces, but agreeing that it tasted 

 sweet. " I did this," said the physician with a smile, " to teach 

 you the importance of observing detail. If you had watched me 

 carefully you would have noticed that I put my first finger in 

 the urine but licked my second finger !" 



It is common knowledge that different people viewing the 

 same scene will notice different things according to where their 

 interests lie. In a country scene a botanist will notice the 

 different species of plants, a zoologist the animals, a geologist 

 the geological structures, a farmer the crops, farm animals, 

 etc. A city dweller with none of these interests may see only 

 a pleasant scene. Most men can pass a day in the company of 

 a woman and afterwards have only the vaguest ideas about what 

 clothes she wore, but most women after meeting another woman 

 for only a few minutes could describe every article the other was 

 wearing. 



It is quite possible to see something repeatedly without register- 

 ing it mentally. For example, a stranger on arrival in London 

 commented to a Londoner on the eyes that are painted on the 

 front of many buses. The Londoner was surprised, as he had 

 never noticed them. But after his attention had been called to 

 them, during the next few weeks he was conscious of these eyes 

 nearly every time he saw a bus. 



Changes in a familiar scene are often noticed even though the 

 observer may not have been consciously aware of the details of 

 the scene previously. Indeed sometimes an observer may be 

 aware that something has changed in a familiar scene without 

 being able to tell what the change is. Discussing this point, 

 W. H. George says : 



" It seems as if the memory preserves something like a photo- 

 graphic negative of a very familiar scene. At the next examina- 

 tion this memory image is unconsciously placed over the visual 

 image present, and, just as with two similar photographic nega- 



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