CHEMICAL ELEMENTS AND ATOMS URBAIN 209 



hj^clrogen, it is by following the capricious trajectories of gamboge 

 particles. 



He probably would not have been concerned with this gap in his 

 demonstration were it not that his scruples made him wish to close 

 it up. He has accumulated excellent presumptions which he has 

 attached to these least apparent parts of our universe. He did not 

 limit himself to those pseudosolutions just mentioned nor to radio- 

 activity. Following Lord Rayleigh, he asked the question of the 

 blue of the sky. He gathered 15 independent ways for the determi- 

 nation of the constant N, which he modestly called Avogadro's 

 number. 



His experiments in this direction are doubtless the most extended 

 that have been made. But he has been able to conclude only that 

 the existence of molecules, and therefore of atoms, is exceedingly 

 probable. In reviewing the matter in most diverse aspects he showed 

 that it is indispensable for coordinating our knowledge. If he has 

 left an indefinitely small amount of doubt as to the reality of the 

 molecule and the atom, he has at least made us like them. He 

 has shown that at present science and poetry — fact and fancy — are 

 not irreconcilable. He has passed on the tradition of Laplace, of 

 Alembert, and of Fontenelle. His spirit fraternizes with that of 

 Lucretius and the bees of Hymettus have placed their honey upon 

 his lips. 



Is it necessary to seek the reality of the atom in the absolute 

 manner of the philosophers? Are not molecules and atoms syntheses 

 which embody the fundamental laws of chemistry and a large 

 part of those of physics? Their reality (as J. Perrin indicated in 

 the last edition of his book on atoms, pp. 294-295) lies in the rela- 

 tionships they allow between phenomena which, without them, we 

 would never coordinate. Were we to strike out to-day from the 

 scientific vocabulary the terms atoms and molecules, all physical- 

 chemical science would disappear, leaving only a dry list of facts 

 impossible to connect one with another. 



The reality of the atom is doubtless relative, but it is probably 

 for the best. It has been justly said that absolute philosophy gives 

 way more and more to relative science. Time is a good example. 

 It allows us to give the atom a relative existence. 



The extreme complication of modern science carries subtleties 

 which we who sit on the school benches may ignore. It is repug- 

 nant to mix these philosophical matters with positive facts. The 

 facts come to us mixed with no hypotheses, and here we find a 

 criterion of the tiidy scientific mind. How difficult it is to attain 

 it! We are given the definition of a chemical element according 

 to Lavoisier, but we talk of it in a very different way. The ultimate 



