Theory of the Chemical Elements. 875 



tli3 scope of the table. In the atom, they may be regarded 

 as partially isolated from the rest, though not preserving 

 their identity so completely as in an ordinary chemical com- 

 pound. A rearrangement typical of radioactive change may 

 be capable of rejecting a group, which may appear as an 

 a particle. It is possible, as we shall see later, to give a 

 speculative theory of some of the radioactive processes on 

 this basis, which, however crude and incapable of verification 

 in its present form, is certainly not in opposition to any of 

 the phenomena known with certainty. Its capacity for veri- 

 cation is, however, in some respects very real, as will appear. 

 The investigation also serves the purpose of indicating some 

 lines on which valuable experiments might, be made. 



As an example of this, we may eite the generally accepted 

 view that all a particles are positively charged atoms of 

 helium. The value of e/m for these particles is not regarded 

 as certainly accurate, and serves merely to indicate that they 

 are of atomic size. The belief that they are helium rests 

 entirely upon the spectroscopic investigations of Ramsay and 

 others with regard to the products of disintegration of niton 

 or radium emanation, and the more recent work of Ruther- 

 ford and Royds referring only to a particular case*. These 

 experiments prove that helium is one of these products, but 

 they certainly do not prove that all the a particles from the 

 radium or thorium series consist of helium. There is. in 

 fact, strong reason to doubt this \ iew. and it will be sufficient. 

 to mention only two facts in this connexion. 



In the first place, not only was the helium spectrum 

 obtained in these experiments, but three other lines, of wave- 

 lengths 6180, 5695, and 5455 which have never been iden- 

 tified. These results have been confirmed, and certainly 

 seem to indicate a gas other than helium or any known 

 terrestrial substance. The same spectrum is found for the 

 gas liberated by solution of radium bromide. 



The excess of hydrogen liberated in experiments with the 

 emanation has also never been explained satisfactorily, and 

 there is some doubt whether it is due entirely to moisture 

 which has found its way into the apparatus. The writer 

 feels compelled to express the belief that some <x particles are 

 not helium, but hydrogen and other substances, more espe- 

 cially nebulium, or more probably Nu 2 . another elementarv 

 gas. and it is very desirable that more spectroscopic work 



* A paper by Rutherford and Boltwood (Phil. Mag. October 1911), 

 which has appeared since this was written, 2'ives much more definite 

 proof, but it again does not show that the helium may not be a modified 

 a particle in many cases. 



