The Evolution of the Sciences 



or even in the interior of the earth, or on the 

 moon, the same mass will invariably be found 

 for the same object. If the object is hot or 

 cold not the slightest difference will be found in 

 its weight, however accurate the measurement 

 may be; consequently heat is something im- 

 material, because its addition to matter leaves 

 the mass unchanged; the object in the same way 

 may be electrified without modifying its weight, 

 hence electricity also is not material. 



Here we have at last the sovereign criterion 

 enabling us to define matter, to trace it every- 

 where, and if we complete our idea by combining 

 with it the notion introduced into science by 

 Lavoisier we shall conclude that matter is inde- 

 structible and imperishable, and that itconstitutes 

 the primordial and perhaps the sole element of 

 the world. Here stands the citadel. It is here 

 that we must strike if we are to overthrow the 

 materialistic conception of the universe, but there 

 remain some outworks to be demolished before 

 the final assault. 



Let us leave for a moment the question of 



mass and turn our attention to the meaning of 



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