6 Preliminary Remarks. 



But let us suppose the air removed or annihilated, and the pro* 

 jectile force (in the direction of a tangent), to be sufficient to carry 

 the stone as far from the earth as gravity would cause it to 

 descend each instant, and the stone would describe a circle 

 round the earth, and if there were nothing to stop or obstruct it, 

 it would thus continue to revolve without end. We have indeed 

 this principle exemplified in the motion of the moon, which re- 

 volves in a void about the earth ; we see moreover the same 

 renewed, perpetual motion in the planets which pass in like man- 

 ner through spaces destitute of all material resistance. We are 

 hence lead to believe that matter is incapable of effecting any 

 change in itself, either with respect to motion or rest, and once 

 put into either of these states, it would continue in this state so 

 long as it should remain undisturbed by any cause foreign to itself. 

 This indifference to motion and rest, this want of all power of 

 self-direction, has obtained the name of inertia. There is one 

 class of bodies, however, that seem to form an exception to this 

 law of matter. It comprehends those which we call animated, 

 which put themselves in motion or stop themselves by an act of 

 the will ; but even in these the material elements which consti- 

 tute their parts or members, and these members themselves, are 

 perfectly inert. It is their union or combination that possesses 

 the quality of life. Separated, they have no longer this power, 

 but return to the condition of ordinary matter. We* are entirely 

 in the dark with regard to the cause of this remarkable difference 

 in the bodies that surround us. As to what constitutes a state of 

 life, we can pretend to no knowledge whatever. But seeing 

 matter under all other circumstances destitute of the power of 

 self-direction, and knowing also that in living beings it loses this 

 faculty by death and by sleep, we are led to regard it as foreign 

 to the essence of matter, and to consider the volition of animated 

 beings, as the act of an immaterial principle which resides within 

 them. We are unable to say in what part this principle is seat- 

 ed, or in what it consi^s, and still less how, being immaterial, it 

 is capable of acting upon matter ; but with the little attention 

 that we have paid to ourselves and to the objects about us, 

 these obscurities, unfortunately too common, in which our imper- 

 fect knowledge has left us, ought not to be made the grounds of 

 an objection against the essence of things with which we must be 

 contented to remain unacquainted. So that we here proceed philo- 

 sophically, according to the rule adopted in other cases, by 



