FORCE. 193 



form of force motion, heat, light, affinity, &c. in 

 each other, with no loss or gain, a necessary part 

 of the order of phenomena,* but another character 

 of force, which is involved in this, is also seen to 

 be necessary, and to be full of a significance of 

 its own. 



FoB>Jf the amount of force is always the same, 

 and every process in which it is concerned is a 

 change merely of its form or place, then every such 

 process must have two aspects : on the one side 

 force comes into play ; on the other, to an 

 exactly equal amount, it ceases. Its operation is 

 always and inevitably an equal plus and minus. 

 There cannot be the one without the other. Every 

 physical process is, necessarily, the adding of force 

 in one direction, the withdrawing it in the opposite, 

 and may be represented by the equivalent, but 

 opposed, motions of the two sides of a balance. 

 This we have seen to be the case in respect to the 



* For the discussion of this suhjcct the reader is referred to 

 Mr. Grove's admirable treatise on the Correlation of the Physical 

 Forces ; it has been briefly treated by the writer in the Cornhill 

 Magazine for October, 1861. 



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