24 CORRELATION OF PHYSICAL FORCES. 



bent spring is freed, when the raised weight falls, a converse 

 series of motions must be effected, and this theory would lead 

 to a mere reciprocation, which would be equally unproduc- 

 tive of permanent change with the annihilation of force. If 

 raising the weight has changed the centre of gravity of the 

 earth, and thence of the universe, the fall of the weight, it 

 will be said, restores the original centre of gravity, and every- 

 thing comes back to its original status. In this argument we 

 again, in thought, isolate our experiment : we neglect sur- 

 rounding circumstances. Between the time of the raising 

 and falling of the weight, be the interval never so small, 

 nay, more, during the rising and during the fall, the earth 

 has been going on revolving round its axis and round the 

 sun, to say nothing of other changes, such as temperature, 

 cosmical magnetism, &c., which we may call accidental, but 

 which, if we knew all, would probably be found to be as 

 necessary and as reducible to law as the motion of the earth. 

 A change having taken place, the fall of the weight does 

 not bring back the status quo, but other changes supervene, 

 and so on. Nothing repeats jtself, because nothing can 

 be placed again in the same condition: the past is irre- 

 vocable. 



