PAET III FOKCE 



The Classical Mechanics. 



THE English teach mechanics as an experimental science; on the 

 Continent it is taught always more or less as a deductive and a priori 

 science. The English are right, no doubt. How is it that the other 

 method has been persisted in for so long; how is it that Continental 

 scientists who have tried to escape from the practice of their predeces- 

 sors have in most cases been unsuccessful ? On the other hand, if the 

 principles of mechanics are only of experimental origin, are they not 

 merely approximate and provisory? May we not be some day com- 

 pelled by new experiments to modify or even to abandon them ? These 

 are the questions which naturally arise, and the difficulty of solution 

 is largely due to the fact that treatises on mechanics do not clearly 

 distinguish between what is experiment, what is mathematical rea- 

 soning, what is convention, and what is hypothesis. This is not all. 



1. There is no absolute space, and we only conceive of relative 

 motion; and yet in most cases mechanical facts are enunciated as if 

 there is an absolute space to which they can be referred. 



2. There is no absolute time. When we say that two periods are 

 equal, the statement has no meaning, and can only acquire a meaning 

 by a convention. 



3. Not only have we no direct intuition of the equality of two 

 periods, but we have not even direct intuition of the simultaneity of 

 two events occurring in two different places. I have explained this in 

 an article entitled " Mesure du Temps." 1 



4. Finally, is not our Euclidean geometry in itself only a kind of 

 convention of language? Mechanical facts might be enunciated with 

 reference to a non-Euclidean space which would be less convenient but 

 quite as legitimate as our ordinary space; the enunciation would be- 

 come more complicated, but it still would be possible. 



Thus, absolute space, absolute time, and even geometry are not con- 

 ditions which are imposed on mechanics. All these things no more 

 existed before mechanics than the French language can be logicallj 

 said to have existed before the truths which are expressed in French. 



i Revue de Metaphysique et de Morale, t. vi., pp. 1-13, January, 1898. 



