OF NATURAL PHILOSOPHY. 223 



duced by it on matter, to say that matter is inert, 

 or has inertia, as it is termed, is only to say that 

 the cause is expended in producing its effect, and 

 that the same cause cannot (without renewal) pro- 

 duce double or triple its own proper effect. In this 

 point of view, equilibrium may be conceived as a 

 continual production of two opposite effects, each 

 undoing at every instant what the other has done. 



(235.) However, if this should appear .too metaphy- 

 sical, at all events this difference of effects gives rise 

 to two great divisions of the science of force, which 

 are commonly known by the names of STATICS 

 and DYNAMICS ; the latter term, which is general, 

 and has been used by us before in its general sense, 

 being usually confined to the doctrine of motion, as 

 produced and modified by force. Each of these 

 great divisions again branches out into distinct sub- 

 divisions, according as we consider the equilibrium 

 or motion of matter in the three distinct states in 

 which it is presented to us in nature, the solid, 

 liquid, and aeriform state, to which, perhaps, ought 

 to be added the viscoiis, as a state intermediate be- 

 tween that of solidity and fluidity, the consideration 

 of which, though very obscure and difficult, offers a 

 high degree of interest on a variety of accounts. 

 Statics and Dynamics. 



(236.) The principles have been definitively fixed 

 by Galileo and his successors, down to Newton, 

 on a basis of sound induction ; and as they are 

 perfectly general, and apply to every case, they 

 are competent, as we have already before ob- 

 served, to the solution of every problem that can 

 occur in the deductive processes, by which pheno- 



