PROGRESSIVE EFFECTS. 31 



all that which follows is diminished. The effect changes, 

 because the cause which it really obeys, the proximate cause, 

 the real cause in fact, has changed. This principle is recog- 

 nised by mathematicians when they enumerate among the 

 causes by which the motion of a body is at any instant deter- 

 mined, the force generated by the previous motion ; an ex- 

 pression which would be absurd if taken to imply that this 

 " force" was an intermediate link between the cause and the 

 effect, but which really means only the previous motion itself, 

 considered as a cause of further motion. We must, therefore, 

 if we would speak with perfect precision, consider each link in 

 the succession of motions as the effect of the link preceding 

 it. But if, for the convenience of discourse, we speak of the 

 whole series as one effect, it must be as an effect produced by 

 the original impelling force ; a permanent effect produced by 

 an instantaneous cause, and possessing the property of self- 

 perpetuation. 



Let us now suppose that the original agent or cause, 

 instead of being instantaneous, is permanent. Whatever effect 

 has been produced up to a given time, would (unless pre- 

 vented by the intervention of some new cause) subsist per- 

 manently, even if the cause were to perish. Since, however, 

 the cause does not perish, but continues to exist and to ope- 

 rate, it must go on producing more and more of the effect ; 

 and instead of an uniform effect, we have a progressive series 

 of effects, arising from the accumulated influence of a perma- 

 nent cause. Thus, the contact of iron with the atmosphere 

 causes a portion of it to rust ; and if the cause ceased, the 

 effect already produced would be permanent, but no further 

 effect would be added. If, however, the cause, namely, ex- 

 posure to moist air, continues, more and more of the iron 

 becomes rusted, until all which is exposed is converted into a 

 red powder, when one of the conditions of the production of 

 rust, namely, the presence of unoxidized iron, has ceased, and 

 the effect cannot any longer be produced. Again, the earth 

 causes bodies to fall towards it, that is, the existence of the 

 earth at a given instant, causes an unsupported body to move 

 towards it at the succeeding instant : and if the earth were 



