2 INTRODUCTION. 



General Physics comprehends, abstractedly, the 

 examination of the properties of those moveable and 

 extended works of creation which we denominate 

 bodies ; that department of it called dynamics in- 

 cludes the consideration of solid bodies, for the 

 purpose of determining mathematically, from a few 

 experiments, the laws which regulate their equili- 

 brium and motion. 



This branch in its different divisions takes the 

 names of Statics, Hydrostatics, Aerostatics, $c, 

 according to the nature of the bodies, the movements 

 of which are examined. 



Optics is confined to the consideration of the par- 

 ticular motions of light, and is a branch of natural 

 philosophy in which experimental knowledge is be- 

 coming daily more necessary to the explication of 

 its numerous phenomena. 



Chemistry, another division of general physics, is 

 the science by which we estimate and account for the 

 changes produced in bodies by the motions of such 

 of their component parts as are too minute to affect 

 the senses individually. The practical part of 

 chemistry may be said to consist in placing bodies 

 in such positions relatively to each other, as are 

 thereby adapted to produce certain changes. It is, 

 therefore, obvious that this science is the result of 

 experiment, and is not reducible to mathematical 

 calculation, or methodical deduction. 



The theory of heat and that of electricity, according 

 to the point of view in which each is considered, ap- 

 pertain almost equally to dynamics and to chemistry. 



