266 THE NATURAL HISTORY [LETT. 



LETTER C. 



TO THK HONOURABLE DAIXES BARRIXGTON. 



THEY wlio write on natural history cannot too frequently advert 

 to instinct, that wonderful, but limited faculty, which, in some 

 instances, raises the brute creation as it were above reason, and 

 in others leaves them so far below it. Philosophers 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 example ; whereas reason, without in- 

 struction, would lead them to 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 conform 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 schoolboy 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 its house with straws and dry grasses, which do not 

 give it that rotundity and compactness so remarkable iu 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 con- 

 trived as to conform to the obstruction, and becomes flat or oval, 

 or compressed. 



In the following instances instinct is perfectly uniform and 

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

 mouse, and the bird called the nut-hatch (Sitla Europcca), which 



