THE CONSERVATION OF ENERGY 



phlogistic chemists recognized the equation between 

 cal. and x, or phlogiston as they called it, and in so do- 

 ing made a great step in advance; but they involved 

 themselves again in a system of mistakes by putting 

 x in place of O. In this way they obtained H = 

 HO + *. 



"Chemistry teaches us that matter, as a cause, has 

 matter for its effect; but we may say with equal justi- 

 fication that to force as a cause corresponds force as 

 effect. Since c = e, and e = c, it is natural to call one 

 term of an equation a force, and the other an effect of 

 force, or phenomenon, and to attach different notions 

 to the expression force and phenomenon. In brief, 

 then, if the cause is matter, the effect is matter; if the 

 cause is a force, the effect is also a force. 



"The cause that brings about the raising of a 

 weight is a force. The effect of the raised weight is, 

 therefore, also a force ; or, expressed in a more general 

 form, separation in space of ponderable objects is a 

 force; and since this force causes the fall of bodies, we 

 call it falling force. Falling force and fall, or, still more 

 generally, falling force and motion, are forces related 

 to each other as cause and effect forces convertible 

 each other two different forms of one and the 

 object. For example, a weight resting on the 

 ;nd is not a force: it is neither the cause of motion 

 nor of the lifting of another weight. It becomes so, 

 however, in proportion as it is raised above the ground. 

 The cause that is, the distance between a weight and 

 the earth, and the effect, or the quantity of motion 

 produced, bear to each other, as shown by mechanics, 

 a constant relation. 



261 



