INTRODUCTION. 



OF NATURAL HISTORY, AND OF SYSTEMS GENERALLY. 



As few persons have a just idea of Natural History, it appears necessary to com- 

 mence our work by carefully defining the proposed object of this science, and establish- 

 ing rigorous limits between it and the contiguous sciences. 



The word Nature, in our language, and in most others, signifies — sometimes, the 

 qualities which a being derives from birth, in opposition to those which it may 

 owe to art ; at other times, the aggregate of beings which compose the universe ; 

 and sometimes, again, the laws which govern these beings. It is particularly in 

 this latter sense that it has become customary to personify Nature, and to emjjloy 

 the name, respectfully, for that of its Author. 



Physics, or Natural Philosophy, treats of the nature of these three relations, and is 

 either general or particular. General Physics examines, abstractedly, each of the 

 properties of those moveable and extended beings which we call bodies. That depart- 

 ment of them styled Dynainics, considers bodies in mass ; and, proceeding from a very 

 small number of experiments, determines mathematically the laws of equilibrium, and 

 those of motion and of its communication. It comprehends in its diflf"erent divisions 

 the names of Statics, Mechanics, Hydrostatics, Hydrodynamics, Pneumatics, &c., ac- 

 cording to the nature of the bodies of which it examines the motions. Optics considers 

 the particular motions of light ; the phenomena of which, requiring experiments for 

 their determination, are becoming more numerous. 



Chemistry, another branch of General Physics, expounds the laws by which the 

 elementary molecules of bodies act on each other when in close j)roximity, tiie com- 

 binations or separations which result from the general tendency of these molecules to 

 unite, and the modifications which diflferent circumstances, capable of separating or 

 approximating them, produce on that tendency. It is a science almost wholly ex- 

 perimental, and which cannot be reduced to calculation. 



The theory of Heat, and that of Electricity, belong almost equally to Dynamics or 

 Chemistry, according to the point of view in which they are considered. 



The method which prevails in all the branches of General Physics consists in 

 isolating bodies, reducing them to their utmost simplicity, in bringing each of their 

 properties separately into action, either mentally or by experiment, in observing or 

 calculating the results, in short, in generalizing and correcting the laws of these pro- 



