1915^ Recent Conceptions of the Atom 121 



found in minerals whicli are radio-active, and in the same year, 

 1903, Ramsay and Soddy established by direct experiment that 

 there is a continuous production of helium from radium. May I 

 not then reaffirm the belief that these monatomic, uncharged 

 gases are all the products of disintegration changes and that the 

 proof will be forthcoming? In fact, the results obtained already 

 by J. J. Thomson, Ramsay, Winchester, Collie, Patterson and 

 Masson, though disputed, and still in doubt, would seem to 

 prove this for neon and argon in addition to the conclusive evi- 

 dence for helium. 



Let us next see something of the relations of the atom to 

 electricity. Dalton's picture of the atom, as we have seen, was 

 that of an exceedingly small central particle of solid matter 

 surrounded by an atmosphere of heat. Davy, in 1807, supposed 

 that these particles were in different electrical states and so ac- 

 counted for chemical affinity — a theory which was later vari- 

 ously elaborated by Berzelius and others. Faraday's law, ac- 

 cording to Helmholtz, tells us that the same definite quantity of 

 either positive or negative electricity moves always with each 

 univalent atom, or with every unit of affinity of a multivalent 

 atom, and accompanies it in all its motions. This quantity we 

 may call the electric charge of the atoms. 



In this same Faraday lecture in 1881, Helmholtz added: 

 " The most startling result of Faraday's law is perhaps this. 

 If we accept the hypothesis that the elementary substances are 

 composed of atoms, we cannot avoid concluding that electricity 

 also, positive as well as negative, is divided into definite ele- 

 mentary portions which behave like atoms of electricity." 



From the earliest stages of the atomic hypothesis in the ef- 

 forts at accounting for affinity and valence, phenomena of com- 

 bination, the vision of the atom became associated with electric- 

 ity and more or less material conceptions grew up as to this in- 

 dispensable and equally indivisible accompaniment. 



This brings us then to the atom of Sir J. J. Thomson, which, 

 as first stated, was simply made up of corpuscles of negative 

 electricity or electrons. Of course, there are two steps in the 

 evolution of this idea. First, it must be established that nega- 



