16 INAUGURAL ADDRESS. 



certain atoms could have the valence zero and that this fact would 

 have to be reckoned with in any future theorising. 



And then, a little later, came that marvellous rush of experi- 

 mental work and startling discovery that originated in Becquerel's 

 observation of the radio-active character of the old metallic element, 

 uranium. Madame Curie and her husband, investigating this, 

 discovered radium as a constant minute ingredient of uranium ores, 

 isolated its compounds, investigated its properties, and determined 

 its place in Mendeleeff's natural classification. The radio-activity 

 of thorium, too, was detected and studied ; and it was found that 

 both thorium and radium give rise to the formation of " emana- 

 tions " or gases, closely resembling in their properties, and especi- 

 ally in their zero valence, those elements of the argon group pre- 

 viously discovered in the atmosphere by Ramsay. Moreover it 

 was found that some of the active " rays " actually consist of 

 electrons or negative electrical atoms, shot off with a velocity 

 comparable to that of light, while others of a grosser kind consist 

 of positively charged material atoms : and these last have been 

 proved to be identical with the atoms of helium. Other products 

 have been obtained in quantities very minute, it is true, but still 

 sufficient to admit of some investigation ; and, in particular, 

 attention has been paid to the rates of decay of their radio-activity. 

 We owe to Rutherford and Soddy conjointly the theory of all these 

 inter-related phenomena — the theory of the spontaneous trans- 

 formations of the atom, whereby new kinds of atom, both electrical 

 and material, are produced ; some of the latter having but a short 

 life before they in turn undergo spontaneous disruption like their 

 parents. Recent as this theory of successive atomic transforma- 

 tions is, it may be regarded as proved : proved by mathematical 

 analysis of quantitative observations, proved by its rational explana- 

 tion of a host of related phenomena, proved by its successful pre- 

 dictions of previously unknown facts. And perhaps the most 

 interesting thing about it is that it confirms and tends to complete 

 the old atomic theory. For, in spite of the etymological signifi- 

 cance of the word atom — that which can't be cut — chemists have 

 long been convinced that each elementary atom must have an 

 internal structure of its own and consist of parts or sub-atoms, 

 much as molecules consist of atoms ; and speculations have long 

 been rife as to how many sorts of sub-atom there may be and 

 whether indeed all atoms do not consist of the same ultimate 

 constituents, combined in different numbers and on different 

 patterns. Some such idea was an unavoidable outcome of the 



