INTRODUCTION. 3 



objects it examines arc sufiiciently 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 

 all its 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 

 higher orders of animals ; a single one being suppressed, every 

 vestige of life is annihilated. 



Dynamics have thus nearly become a science of pure calcu- 

 lation ; 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 natural history, 

 which it uses with advantage on many occasions; it is that of 

 the conditio?iSiof existence^ commonly styled fmal causes. As 

 nothing can exist without the re-union of those conditions 

 which render its existence possible, tlie component parts of 

 each being must be so arranged as to render possible the whole 



