180 ESSAYS BIOGRAPHICAL AND CHEMICAL 



theses that he ventures to construct a theory. He has a 

 rooted horror of fiction in the wrong place, and he dreads 

 lest his hypothesis should turn out to be misplaced 

 fiction. 



I have thought it better to begin by these somewhat 

 abtruse remarks, in order to place what I propose to 

 discuss on a true basis. It is to be understood that any 

 suppositions which I shall make use of are of the nature 

 of hypotheses, devised solely because they may prove 

 useful. Events are not yet ripe for a theory. 



It will be remembered that Professor Rutherford and 

 Mr. Soddy announced a ' view ' that certain elements 

 which possess the power of discharging an electroscope, 

 and which are therefore called ' radioactive/ are suffering 

 disintegration that is, they are splitting up into other 

 elements, only one of which has as yet been identified. 

 Three of these elements, namely, radium, thorium, and 

 actinium, early in the process of disintegration give off an 

 ' emanation,' or supposed gas ; the proof of the gaseous nature 

 of these emanations is that they can be confined by glass 

 or metal, like gases, and that they can be liquefied or 

 solidified when cooled to a sufficiently low temperature. 

 It is necessary to pay attention to this peculiarity; for 

 these radioactive elements, and two others, uranium and 

 polonium, also give off' so-called /3-rays, which penetrate 

 glass and metal, and which are believed from the dis- 

 coveries of Professor J. J. Thomson and others to be 

 identical with negative electricity. 



Now Rutherford and Soddy, reasoning on the premises 

 that radium was always found associated with uranium 

 and thorium, and also that the ores of these metals, 

 pitchblende and thorite, had been found to contain the 

 gas helium, made the bold suggestion, ' The speculation 

 naturally arises whether the presence of helium in minerals 

 and its invariable association with thorium and uranium 



