482 PRINCIPLES OF CHEMISTRY 



came to light a foil hundred years later than the immortal principles of 

 Newton. 5 



From the foregoing, as well as from the failures of so many attempts at 

 finding in experiment and speculation a proof of the compound character of 

 the elements and of the existence of primordial matter, it is evident, in my 

 opinion, that this theory must be classed among mere Utopias. But Utopias 

 can only be combated by freedom of opinion, by experiment, and by new 

 Utopias. In the republic of scientific theories freedom of opinions is guaran- 

 teed. It is precisely that freedom which permits me to criticise openly the 

 widely-diffused idea as to the unity of matter in the elements. Experiments 

 and attempts at confirming that idea have been so numerous that it really 

 would be instructive to have them all collected together, if only to serve as a 

 warning against the repetition of old failures. And now as to new Utopias 

 which may bo helpful in the struggle against the old ones, I do not think it 

 quite useless to mention & phantasy of one of my students who imagined that 

 the weight of bodies does not depend upon their mass, but upon the character 

 of the motion of then* atoms. The atoms, according to this new Utopian, may 

 all be homogeneous or heterogeneous, we know not which ; we know them 

 in motion only, and that motion they maintain with the same persistence as 

 the stellar bodies maintain theirs. The weights of atoms differ only in con- 

 sequence of their various modes and quantity of motion ; the heaviest atoms 

 may be much simpler than the lighter ones : thus an atom of mercury may 

 be simpler than an atom of hydrogen the manner in which it moves causes 

 it to be heavier. My interlocutor even suggested that the view which 

 attributes the greater complexity to the lighter elements finds confirmation 

 in the fact that the hydrocarbon radicles mentioned by Pelopidas, while 

 becoming lighter as they lose hydrogen, change their properties periodically 

 in the same manner as the elements, change theirs, according as the atoms 

 grow heavier. 



The French proverb, La critique est facile, mais I'art est difficile, how- 

 ever, may well be reversed in the case of all such ideal views, as it is much 

 easier to formulate than to criticise them. Arising from the virgin soil of 

 newly-established facts, the knowledge relating to the elements, to their 

 masses, and to the periodic changes of their properties has given a motive 

 for the formation of Utopian hypotheses, probably because they could not be 

 foreseen by the aid of any of the various metaphysical systems, and exist, 

 like the idea of gravitation, as an independent outcome of natural science, 

 requiring the acknowledgment of general laws, when these have been estab- 

 lished with the same degree of persistency as is indispensable for the accept- 

 ance of a thoroughly established fact. Two centuries have elapsed since the 

 theory of gravitation was enunciated, and although we do not understand its 

 cause, we still must regard gravitation as a fundamental conception of natural 

 philosophy, a conception which has enabled us to perceive much more than 

 the metaphysicians did or could with their seeming omniscience. A hundred 



5 It is noteworthy that the year in which Lavoisier was born (1748) the author of 

 the idea of elements and of the indestructibility of matter is later by exactly one 

 century than the year in which the author of the theory of gravitation and mass was born 

 (1643 N.3.). The affiliation of the ideas of Lavoisier and those of Newton is beyond doubt. 



