44 POPULAR SCIENCE MONTHLY 



Grant that we have discovered particles — in round numbers one 

 thousandth part the size and weight of the hydrogen atom — the argu- 

 ment is still not complete for the divisibility of the atom. Perhaps we 

 have found a new element. But cathode rays were produced under 

 circumstances where they must have arisen from the cathode itself, and 

 it is hard to escape from the conclusion that the atoms of the cathode 

 disintegrated to a certain extent to furnish these particles. Further- 

 more, rays have been studied having as their sources different metals 

 under the influence of electrical currents, different metals heated 

 to incandescence, flames of different kinds and ultra-violet light; and 

 these rays appear to consist of corpuscles of the same weight, no 

 matter what their source. This makes it difficult to escape from the 

 further conclusion that atoms of a great variety of natures are capable 

 of disintegrating and of furnishing the same product by the disintegra- 

 tion ; 4 and this is as much as to say that instead of about eighty differ- 

 ent elements we have one ' mother substance,' and Prout's hypothesis 

 is once more very much alive, somewhat modified, it is true, and in a 

 new garb, better suited to the present fashions. 



It remains to rehearse briefly the evidence to be obtained from 

 radio-active phenomena. In the first place, the rays incessantly sent 

 out from these extraordinary substances consist, at least in part, of 

 rays like the cathode rays, and are streams of the same kind of cor- 

 puscles, but, on the whole, traveling with greater velocities than the 

 corpuscles of the cathode rays. It has been proved by Eutherford and 

 Soddy that the emission of the radiations from these substances is 

 accompanied by a disintegration, or decay, as they describe it, of the 

 substances themselves. These investigators have caught some of the 

 products of this decay and have studied their properties. These prod- 

 ucts themselves deca} r , some slowly, some rapidly, sending forth other 

 rays and furnishing new products to decay in turn. Indeed each new 

 issue of a scientific journal for the past few years seems to chronicle 

 the birth, life and death of a fresh radio-active substance. The rate 

 at which new offspring of radium, thorium and allied elements are 

 discovered and studied during their fleeting existences reminds one of 

 nothing so much as the genealogy of Noah as given in the fifth chapter 

 of Genesis. 5 



4 Experimental details, and also comprehensive treatments of the subject 

 as a whole and of special parts, may be found in three books by J. J. Thomson: 

 'The Discharge of Electricity through Gases' (based on lectures given at 

 Princeton University in October, 1896); 'Conduction of Electricity through 

 Gases' (a larger book); 'Electricity and Matter' (lectures delivered at Yale 

 University in 1903). 



B It is an indication of the widespread interest in this subject, and of the 

 activity of the workers in this field, that one journal, in the year 1905, con- 

 tained no less than 167 abstracts of articles upon radioactive phenomena. E. 

 Rutherford's book, ' Radio-activity,' 2d edition, 1905, is a masterly survey of 

 the whole subject. 



