250 NATURAL HISTORY 



LETTER LVI. 



TO THE SAME. 



THEY who write on natural history cannot too frequently 

 advert to instinct, that wonderful limited faculty, which, in 

 some instances, raises the brute creation as it were above 

 reason, and in others leaves them so far below it. Philo- 

 sophers have defined instinct to be that secret influence by 

 which every species is impelled naturally to pursue, at all 

 times, the same way or track, without any teaching or exam- 

 ple ; whereas reason, without instruction, would often vary 

 and do that by many methods which instinct effects by one 

 alone. Now this maxim must be taken in a qualified sense ; 

 for there are instances in which instinct does vary and con- 

 form to the circumstances of place and convenience. 



It has been remarked that every species of bird has a mode 

 of nidification peculiar to itself; so that a school-boy would 

 at once pronounce on the sort of nest before him. This is the 

 case among fields and woods, and wilds ; but, in the villages 

 round London, where mosses and gossamer, and cotton from 

 vegetables, are hardly to be found, the nest of the chaffinch has 

 not that elegant finished appearance, nor is it so beautifully 

 studded with lichens, as in a more rural district : and the wren 

 is obliged to construct it's house with straws and dry grasses, 

 which do not give it that rotundity and compactness so re- 

 markable in the edifices of that little architect. Again, the 

 regular nest of the house-martin is hemispheric ; but where a 

 rafter, or a joist, or a cornice, may happen to stand in the 

 way, the nest is so contrived as to conform to the obstruc- 

 tion, and becomes flat or oval, or compressed. 



In the following instances instinct is perfectly uniform and 

 consistent. There are three creatures, the squirrel, ^field- 

 mouse, and the bird called the nut-hatch, (sit fa Europcea), 



