ENERGY IN GENERAL. 69 



garment; in a word, that something active and 

 permanent subsists in the passage from one condition 

 to another, and that what has changed is only the 

 aspect, the appearance. 



This constant something which is perceived beneath 

 the inconstancy and the variety of forms, and which 

 circulates in a certain manner from the antecedent 

 phenomenon to its successor, is energy. 



But still this is only a very vague view, and it may 

 seem arbitrary. It may be made more exact by 

 examples borrowed from the different categories of 

 natural phenomena. There are energetic modalities 

 in relation with the different phenomenal modalities. 

 The different orders of phenomena which may be 

 presented — mechanical, chemical, thermal, electrical — 

 give rise to corresponding forms of energy. 



When to a mechanical phenomenon succeeds a 

 mechanical, thermal, or electrical phenomenon, we 

 say, embracing transformation in its totality, that 

 there has been a transformation of mechanical energy 

 into another form of energy, mechanical, thermal, or 

 electrical, etc. 



This idea becomes more precise if we examine 

 successively each of these cases and the laws which 

 regulate them. 



§ 3. Mechanical Energy. 



Mechanical energy is the simplest and the oldest 

 known. 



Mechanical Elements : Time, Space, Force, Work. 

 Power. — Mechanical phenomena may be considered 

 under two fundamental conditions — time and space, 



