INTRODUCTION. 



iVs correct ideas respecting natural history are not very generally formed, 

 it appears necessary to begin by defining its peculiar object, and establish- 

 ing rigorous limits between it and neighbouring sciences. 



In our language, and in most others, the word nature is variously em- 

 ployed. At one time it is used to express the qualities a being derives 

 from birth, in opposition to those it may owe to art; at another, the entire 

 mass of beings which compose the universe; and at a third, the laws 

 which govern those beings. It is in this latter sense particularly that we 

 usually personify nature, and, through respect, use its name for that of its 

 Creator. 



Physics, or Natural Philosophy, treats of the nature of these three re- 

 lations, and is either general or particular. General physics examines 

 abstractedly each of the properties of those moveable and extended beings 

 we call bodies. That branch of them styled Dynamics, considers bodies 

 in mass; and, proceeding from a very small number of experiments, de- 

 termines mathematically the laws of equilibrium, and those of motion and 

 of its communication. Its different divisions are termed Statics, Hydro- 

 statics, Hydrodynamics, Mechanics, &c. &c., according to the nature of 

 the particular bodies whose motions it examines. Optics considers the 

 particular motions of light, whose phenomena, which hitherto nothing but 

 experiment has been able to determine, are becoming more numerous. 



Chemistry, another branch of general physics, exposes the laws by which 

 the elementary molecules of bodies act on each 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 separating or approximating them produce on that tendency. It is 

 purely a science of experiment, and is irreducible to calculation. 



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. 



VOL. I. A 



