INTRODUCTION. 3 



mistry 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 employed 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 perfection. 



Calculation, if we may so express it, thus commands nature, and deter- 

 mines 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 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 must be so arranged as to render possible the whole 

 being, not only with regard to itself but to its surrounding relations. The 

 analysis of these conditions frequently conducts us to general laws, as cer- 

 tain as those that are derived from calculation or experiment. 



It is only when all the laws of general physics and those which result 

 from the conditions of existence are exhausted, that we are reduced to the 

 simple laws of observation. 



The most effectual method of obtaining these, is that of comparison. 

 This consists in successively observing the same bodies in the different 

 positions in which nature places them, or in a mutual comparison of dif- 

 ferent bodies ; until we have ascertained invariable relations between their 

 structures and the phenomena they exhibit. These various bodies are 

 kinds of experiments ready prepared by nature, who adds to or deducts 

 from each of them different parts, just as we might wish to do in our labo- 

 ratories ; shewing us, herself, at the same time their various results. 



In this way we finally succeed in establishing certain laws by which 

 these relations are governed, and which are employed like those that are 

 determined by the general sciences. 



The incorporation of these laws of observation with the general laws, 

 either directly or by the principle of the conditions of existence, would 

 complete the system of the natural sciences, in rendering sensible in all 

 its parts the mutual influence of every being. To this end, should these 

 who cultivate these sciences direct all their efforts. 



AH researches of this nature, however, pre-suppose means of distin- 

 guishing clearly, and causing others to distinguish, the bodies they are 

 occupied with ; otherwise we should be continually confounding them. 

 Natural history then should be based on what is called a system of nature — ■ 

 a2 



