Nomenclature of Ornithology. 197 



spicuously above that continued outline in which nature disposes 

 her living groups. These afford me sufficient prominency of cha- 

 racter for my ideal divisions; for ideal they must be, where nature 

 shows none. And thus it is that I can conceive my groups to be at 

 once separate and united ; separate at their typical elevations, but 

 united at their basal extremes. 



It is difficult to convey, in terms sufficiently explicit, an accurate 

 definition of abstract notions like the present. We may see the 

 subject clearly ourselves, but not be able to communicate it by 

 words sufficiently intelligible, unless to those who may happen to 

 view it in the same light as ourselves. I shall therefore take a 

 familiar illustration, which comes home to the feelings of every 

 man, and where it will be immediately apparent that strongly 

 marked divisional groups may be kept apart from each other in 

 our conceptions, although we can recognise no absolute boundary 

 lines by which we can say they are separated . 



Let us take for instance that period of time which involves the 

 annual revolution of the earth round the sun, and let us divide it 

 into the usual departments which we call seasons. Every man 

 can picture to his own mind the decided characters by which these 

 divisions of the year are parted from each other : he can mark out 

 by definite distinctions those striking periods where the year bursts 

 forth into bud, where it opens into flower, where it ripens into 

 fruit, and where it lapses into decay. He can ascertain the na- 

 ture of the impressions which each season forces upon his own 

 feelings, he can communicate such sensations to others, and he can 

 embody those natural periods, of whose separate existence he 

 feels conscious, into separate and well characterized divisions, to 

 which he can refer without fear of being misunderstood, under 

 the distinct appellations of Spring, or Summer, of Autumn, or of 

 Winter. But can he at the same time point out the actual limits 

 of these natural departments of the year ? Can he fix for instance, 

 in that intervening interchange of season, where the rigour of 

 winter silently and imperceptibly relaxes into the mildness of 

 spring, — can he fix, I say, upon the exact period when the former 

 terminates, and the latter begins ? Can he assert at one moment 

 that he is within the precincts of one season, and that, even while 

 he speaks, he has passed into the confines of the other. He may, 



