k5 INTRODUCTION. 



other; the combinations or separations which result from the 

 general tendency of these molecules to re-unite; and the 

 modifications which the various circumstances capable of se- 

 parating or approximating them produce on that tendency. It 

 is purely a science of experiment;, and is irreducible to calcu- 

 lation. 



The theory of heat and that of electricity belong either to 

 dynamics or chemistry, according to the point of view in 

 which they are considered. 



The ruling method in all the branches of general physics 

 consists in isolating bodies, reducing them to their greatest 

 simplicity, in bringing each of their properties separately into 

 action, either by reflection or experiment, and by observing 

 or calculating the results ; and finally, in generalising and con- 

 necting the laws of these properties, so as to form codes, 

 and, if it were possible, to refer them to one single principle 

 into which they might all be resolved. 



The object of Particular Physics, or of J^atural History 

 for the terms are synonymous is the special application of 

 the laws recognised by the various branches of general phy- 

 sics to the numerous and varied beings which exist in nature, 

 in order to explain the phenomena which each of them pre- 

 sents. 



Within this extensive range, astronomy also would be in- 

 cluded ; but that science, sufficiently elucidated by mechanics, 

 and completely subjected to its laws, employs methods, differ- 

 ing too widely from those required by natural history, to per- 

 mit it to be cultivated by the students of the latter. 



Natural history, then, is confined to objects which do not 

 allow of exact calculation, nor of precise measurement in all 

 their parts. Meteorology also is substracted from it and united 

 to general physics ; so that, properly speaking, it considers only 

 inanimate bodies called minerals, and the different kinds of 

 living beings, in all of which we may observe the effects, more 

 or less various, of the laws of motion and chemical attraction, 

 and of all the other causes analysed by general physics. 



Natural history, in strictness, should employ similar methods 

 with the general sciences ; and it does so, in fact, whenever the 



