THE TERRESTRIAL DISTRIBUTION OF RADIUM 25 



earth, for, involving as they would the emission of energy, they 

 would aggravate the very difficulty we are attempting to avoid. 

 We may therefore reasonably conclude that the radioactive 

 elements are not formed in the earth's interior from other 

 elements, although, if they are already present, their decay may, 

 nevertheless, be more or less inhibited. 



The experimental evidence indicates on the part of the 

 radioactive elements an utter disregard for all the changes in 

 physical environment to which we can subject them. The effect 

 of temperature has been investigated by several observers, 1 and 

 their results lead to the final conclusion that atomic trans- 

 formation proceeds at the same rate at all temperatures between 

 — i86°C. (liquid air) and 1,500° C. Quite recently Giebeler 2 

 found lines in the spectrum of Nova Geminorum (2), which have 

 been identified with those of uranium, radium, and radium- 

 emanation, and Dyson 3 has shown that similar lines can be 

 observed in the spectrum of the sun's chromosphere. It would 

 therefore appear that radioactivity is not inhibited by a 

 temperature of 6,ooo° C. or 7,000° C. It has been found that 

 pressures ranging to 2,000 atmospheres are without influence on 

 the activity of radium. Radium emanation introduced into a 

 high-pressure bomb was unaffected by a temperature of 

 2,500° C. and a pressure of 1,000 atmospheres. 



Two other types of phenomena lead to apparently different 

 conclusions. All elements are known to emit electrons when 

 under the influence of ultra-violet light, which indicates that 

 the atom is not altogether indifferent to external influences. 

 Further, the vibrations which give rise to spectrum lines are 

 damped slightly by increase of pressure, so that the lines are 

 displaced towards the red. Strictly, however, this phenomenon 

 is due less to pressure as such than to increase of density {i.e. 

 closer packing of the molecules), for, as Larmor has pointed out, 

 mechanical pressure arises from the translatory motions of 

 molecules, which are too slow to have any detectable influence 

 upon radiation periods. As the density is increased, however, 

 the electrons to which the radiations are due are brought into 

 closer association with surrounding electrons, and the vibrations 



1 Rutherford, Radioactive Substances, p. 502, 191 3. Russell, Proc. Roy. Soc, 

 A., vol. lxxxvi. p. 240, 1912. 



' Astr. Nachr., 191, no. 4,582, June 1912. 

 3 Ibid., 192, no. 4,589, July 191 2. 



