6 INTRODUCTION. 



without comparison, we must observe attentively 

 the same body in the various positions in which it 

 is at different times placed by nature ; and we must 

 compare different bodies with each other, until we 

 can recognise any invariable relations which may 

 exist between their structure and the phenomena 

 which they exhibit. Thus may such bodies, when 

 diligently observed and carefully compared with 

 each other, be considered as experiments ready pre- 

 pared by the hand of nature, who may be supposed 

 to add to or subtract from each in the manner the 

 experimentalist does in his laboratory with the inert 

 materials subject to his control, and herself to pre- 

 sent us with the result of such additions or sub- 

 tractions. 



By these means we may arrive at a knowledge 

 of the laws which regulate the phenomena of na- 

 tural history, strictly speaking, subject to our obser- 

 vation, and which are employed by the great Go- 

 vernor of the universe with the same determinate 

 precision as those which are opened to our view by 

 the general sciences. 



When we have once united the laws of observa- 

 tion with the general laws of matter, and with the 

 conditioo of existence, a system of natural science 

 will ba complete, and we shall then perceive and 

 feel the mutual influence that prevails throughout 

 the works of nature. This is the grand desidera- 

 tum, to obtain which the efforts of naturalists should 

 be steadily directed. 



But all researches by observation and comparison 



