SPECIFIC CHAEACTEKS OF BIRDS. 
523 
from the endless combinations which they undergo, it be-^ 
comes, in many cases, impossible to express, and even dif- 
ficult to perceive, their true relations. When we see such 
vague and indeterminate expressions, as, cmereus^ cineras- 
cens^ albus^ albicans^ niger, nigricans^ fuscus^f usco-7iigri-. 
cans, viridisv, irescens, ruber, rufus, rubicundus, riibescens, 
rosaceus, aureus, aneus, luteus, and find that each of these 
terms, as applied to different species of birds, includes a 
great variety of tints, differing widely from each other, we 
cannot but perceive that no precise ideas have been at- 
tached to them. A general objection, therefore, to the use 
of colour as affording specific distinctions, is, that however 
people may agree with regard to the principal colours, such 
as white, black, brown, blue, scarcely two individuals will 
be found who have precisely the same ideas with regard to 
many or most of the almost innumerable tints with which 
the hand of Nature has pencilled the plumage of the aerial 
wanderers. The ideas even of the best writers on this sub- 
ject have been, and stiil continue to be, very confused, and 
their descriptions of colours are often at utter variance, not 
only with those of others, but even with their own depic- 
tions. This, however, may be thought to form no true 
objection : were the statement correct, as it is believed to 
be, it might not, after all, form an insuperable bar to the 
use of such characters ; for objects, as apparently beyond 
the reach of investigation, have been illustrated, and even 
specified, with great precision. And although a philoso- 
phical arrangement of colours be still a desideratum in 
science, it is a desideratum which may be supplied, when 
persons qualified for the undertaking shall direct their at- 
tention to it. 
The colour of the feathers, however, as has been shewn, 
and as is pretty generally felt, being deficient as a character 
