SIDE I.IGHTS ON BIRDS 



think of a new sense and of what it might reveal — 

 a sense as distinct from the known five as hearing 

 — let us say — is from seeing is an impossible feat. 

 But if we cannot imagine a sixth sense we can 

 at least picture the condition of mankind if they 

 had been deprived of any one of the familiar five. 

 We will cheat the human race of hearing, for 

 example, leaving this channel open to the lower 

 animals. You, to whom the fact of sound has 

 never been vouchsafed, are out with your dog, 

 and suddenly you see that the animal's attention 

 is arrested. His ears prick, his whole attitude 

 is strained. " That dog sees or smells some- 

 thing," you exclaim. Yet your own eyes survey 

 the long stretch of road that is clearly void. 

 Soon a wagon turns the distant corner. Now 

 you ask yourself, " how came that dull brute 

 thus to peer into the future : to foreknow this 

 coming event? " Then, it may be, you forthwith 

 endow him with an acuity of vision that can 

 look through stone walls, or with powers of scent 

 that can catch odoriferous particles blowing dead 

 against the wind. Yet one additional sense 

 makes the matter clear. The dog merely heard 

 the rumbling of the distant wheels. 



In dealing with the manner in which certain 

 insects find their mates, and in which vultures 

 discover hidden carcasses at incredible distances, 

 as well as with the facts of migration, we often 

 reason exactly as men would to whom"' an im- 

 portant sense had been denied. We see wonders 

 enacted before our eyes, and we strain the idea of 

 our own five senses to breaking point in order to 

 account for them. 



The oak-eggar moths travelling from the 

 heathery districts where they resort, will cover 

 distances of several miles, and facing adverse 

 winds, will discover females of their own species 



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