268 Notices respecting New Books. 



*ipon matter. Those who carefully contemplate the process 

 of that gradual refinement of ls.nguage, which results from 

 the necessary demands occasioned by the progress of civili- 

 sation, will see how requisite it is to appropriate terms ori^ 

 ginally of a laxer or of a grosser signification, to some pe- 

 culiar modification of thought ; and hence, that such words 

 as poller and force, primariiv used to denote animal energy, 

 are now, bv a natural extension, grounded upon an obvious 

 analogy, employed to express efficiency in general. In the 

 philosophical acceptation, then, he defines force or power to 

 be that, whatever it be, ** which causes a change in the state 

 of a body, whether that state be rest or motion : and this 

 definition does not require entering into any metaphysical 

 disquisitions relative to the nature of causes, or the connec^^ 

 tion of cause and eflect : that every effect is brought about 

 by some cause, or something which precedes in the order of 

 occurrence, is a truth v/hich none will be disposed to deny; 

 but what is the agency, or where it actually resides, we can 

 seldom know, except, perhaps, in the case of our own vo- 

 luntary actions. It is not, then, the business of the mechar- 

 nist, strictly speaking, to inquire into the modus operandi : 

 we learn, from universal experience, that the muscular energy 

 of animals, the operation of gravity, electricity, pressure, im- 

 pact, &c. are sources of motion, or of modifications of motion ; 

 and hence, without pretending to know the essence of either 

 of these, we do not hesitate to call them mechanical forces ; 

 because it is incontrovertible that bodies exposed to the free 

 action of either, are put into motion, or have the state of 

 their motion changed. Forces, therefore, bemg known to 

 us only by their effects, can only be measured by the effects 

 they produce in like circumstances, whether those effects 

 be creating, accelerating, retarding, deflecting, or preventing 

 motions: and it is by comparing these effects, or by referring 

 them to some common measure of ready appreciation, not 

 bv ascertaining the essential nature of any forces, that me- 

 chanics is made one of the matheniatical sciences. 



'' Besides, what is meant oy the nature of any thing ? As 

 we are io-norant o^its essence, or what makes it that thing 

 and no other thing, we must content ourselves with the dis- 



cov'ery 



