CHAPTEE VIII. 



THE TRANSFORMATION AND EQUIVALENCE OF FORCES. 



66. WHEN, to the unaided senses, Science began to 

 add supplementary senses in the shape of measuring instru- 

 ments, men began to perceive various phenomena which eyes 

 and fingers could not distinguish. Of known forms of force, 

 minuter manifestations became appreciable; and forms of 

 force before unknown were rendered cognizable and meas- 

 ureable. Where forces had apparently ended in nothing, 

 and had been carelessly supposed to have actually done so, 

 instrumental observation proved that effects had in every 

 instance been produced: the forces reappearing in new 

 shapes. Hence there has at length arisen the inquiry 

 whether the force displayed in each surrounding change, 

 does not in the act of expenditure undergo metamorphosis 

 into an equivalent amount of some other force or forces. 

 And to this inquiry experiment is giving an affirmative an- 

 swer, which becomes daily more decisive. Meyer, Joule, 

 Grove and Helmholtz are more than any others to be cred- 

 ited with the clear enunciation of this doctrine. Let us 

 glance at the evidence on which it rests. 



Motion, wherever we can directly trace its genesis, we 

 find to pre-exist as some other mode of force. Our own vol- 

 untary acts have always certain sensations of muscular 

 tension as their antecedents. When, as in letting fall a re- 

 laxed limb, we are conscious of a bodily movement requiring 

 no effort, the explanation is that the effort was exerted in 



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