32 POPULAR SCIENCE MONTHLY. 



the writer, but the results, so far obtained, are negative in character, 

 although if radium were produced at the rate to be expected from 

 theory, it should very readily have been detected.* Such experiments, 

 however, taken over a period of a few months are not decisive, for it 

 is by no means improbable that the parent element may pass through 

 several slow changes, possibly of a ' rayless ' character, before it is 

 transformed into radium. In such a case, if these intermediate 

 products are removed by the same chemical process from the parent 

 element, there may be a long period of apparent retardation before 

 the radium appears. The considerations advanced to account for 

 radium apply equally well to actinium, which, in all probability, when 

 isolated will prove to be an element of the same order of activity as 

 radium. The most important problem at present in the study of 

 radioactive minerals is not the attempt to discover and isolate new 

 radioactive substances, but to correlate these already discovered. Some 

 progress has already been made in reducing the number of different 

 radioactive substances and in indicating the origin of some of them. 

 For example, there is no doubt that the ' emanating substance ' of 

 Giesel contains the same radioactive substance as the actinium of 

 Debierne. In a similar way, there is very strong evidence that the 

 active constituent in the polonium of Mme. Curie is identical with 

 that in the radio-tellurium of Marckwald. The writer has recently 

 shown that the active constituent in radio-tellurium or polonium is, 

 in all probability, a disintegration product of radium (radium E). 

 The same considerations apply to the radio-lead of Hofmann, which 

 is probably identical with the product radium D. It still remains to 

 be shown whether or not there is any direct family connection between 

 the radioactive substances uranium, thorium, radium and actinium. 

 It seems probable that some at least of these substances will prove to 

 be lineal descendants of a single parent element, in the same way that 

 the radium products are lineal descendants of radium. The subject 

 is capable of direct attack by a combination of physical and chemical 

 methods, and there is every probability that a fairly definite answer 

 will soon be forthcoming. 



Radioactivity of the Earth and Atmosphere. 



It is now well established, notably by the work of Elster and 

 Geitel, that radioactive matter is widely distributed both in the earth's 

 crust and atmosphere. There is undoubtedly evidence of the presence 

 of the radium emanation in the atmosphere, in spring water, and 

 in air sucked up through the soil. It still remains to be settled 

 whether the observed radioactivity of the earth's crust is due entirely 



* In a recent letter to Nature, Soddy states that he has found that there 

 is a slow growth of radium in a uranium solution. A similar result has been 

 noted by Whetham. 



