ENERGY IN GENERAL. 65 



saying that fundamentally there is only one objective 

 reality, energy. 



Philosophical Point of View. — But from the philo- 

 sophical point of view are there objective realities? 

 That is a wider question which throws doubt upon 

 matter itself, and which it is not our place to investi- 

 gate here. A metaphysician may always discuss and 

 deny the existence of the objective world. It may- be 

 maintained that man knows nothing beyond his 

 sensations, and that he only objectivates them and 

 projects them outside himself by a kind of hereditary 

 illusion. We must avoid taking sides in all these 

 difficulties. Physics for the moment ignores them — 

 i.e., postpones their consideration. 



In a first approximation we agree to consider 

 ponderable matter only. Chemistry acquaints us 

 with its different forms. They are the different 

 simple bodies, metalloids, metals, and the compound 

 bodies, mineral or organic. Hence we may say that 

 chemistry is the Jiistory of the transformations of 

 matter. From the time of Lavoisier this science has 

 followed the transformations of matter, balance in 

 hand, and ascertains that they are accomplished 

 without change of weight. 



Law of the Conservation of Matter. — Imagine a 

 system of bodies enclosed in a closed vessel, and the 

 vessel placed in the scale of a balance. All the 

 chemical reactions capable of completely modifying 

 the state of this system have no effect upon the scale 

 of the balance. The total weight is the same before, 

 during, and after. It is precisely this equality of 

 weight which is expressed in all the equations with 

 which treatises on chemistry are filled. 



From a higher point of view we recognize here, in 



