, ‘ iw 8 
F 
# 
* 
INTRODUCTION. 3 
, objects it examines are sufliciently simple to allow it. This, 
~ however, is but very rarely the case. 
An essential difference between the general sciences and 
natural history is, that in the former, phenomena are examin- 
_ed, whose conditions are all regulated by the examiner, in 
order, by their analysis, to arrive at general laws; whereas, 
In the latter, they take place under circumstances beyond the 
control of him who studies them for the purpose of discover- 
ing/amid the complication, the effects of known general laws. 
He is not, like the experimenter, allowed to subtract them suc- 
cessively from each condition, and to reduce the problem to 
its elements—he is compelled to take it in its entireness, with 
~ albits conditions at once, and can perform the analysis only in 
thought. Suppose, for example, we attempt to insulate the 
numerous phenomena which compose the life of any of the 
Ai her orders of animals; a single one being Suppncsad every 
* vestige of life is Seimhillteedl 
~ Dynamics have thus nearly become a science of pure calcu- 
tions chemistry is still a science of, pure experiment; and 
natural history, in a great number of its branches, will long 
remain one of pure observation. 
*. These three terms sufficiently designate the methods em- 
ployed in the three branches of the natural sciences; but in 
establishing between them very different degrees of certitude, 
they indicate, at the same time, the point to which they should 
incessantly tend, in order to attain nearer and nearer to per- 
fection. 
_ Calculation, if we may so express it, thus commands nature, 
and determines her phenomena more exactly than observation 
can make them known; experiment compels her to unveil; 
while observation pries into her secrets when refractory, and 
endeavours to surprise her. 
There is, however, a principle peculiar to natur al history; 
which it uses with advantage on many occasions; it is that of 
the conditions of existence, commonly styled final causes. As 
nothing can exist without. the re-union of those conditions 
which render its existence possible, the component parts of 
each.being musf be so arranged as to render possible the whole 
