346 PROCEEDINGS OF SECTION D. 



non-active elements in the evolution of the elements as enunciated 

 primarily by Soddy. 



If the radio-active elements are thus dissipating their substance 

 and changing into non-active elements, the production of radio- 

 activity must be waning in nature, and there must also be a definite, 

 if remote, time when it will cease entirely. The quantity of existing 

 radio-active elements must have been greater in the past, prior to 

 their evolution into the commoner elements, and their distribution 

 would naturally have been of far vaster extent than in the present 

 era. 



Each radio-active particle fires off radio-activity in all direc- 

 tions, and there must be, so to speak, an atmosphere of radio- 

 activity. In the present state of knowledge, it thus appears that 

 .at some future date, millions of years probably, this natural radio- 

 active atmosphere must fail. By reasoning backwards, it is also 

 ■evident that the natural radio-active atmosphere of the past must 

 have been far more excessive and intense than it is in the present, 

 and in the earliest periods it must have been most excessive. 



Some of the physical properties of the different forms of activity 

 are of immediate importance in this paper, n, ji and 7 rays are 

 all capable of absorption by the interposition, in their course, of 

 screens of various thicknesses, and elemental composition, but the 

 coefficient of absorption for each form of rav varies : a rays as 

 generated by radium are completely absorbed by 7 cms. of air, ji 

 rays require up to 4 metres, depending on the hardness of the fi 

 rays ; but 7 rays require great thicknesses of metals to absorb or 

 inhibit their course. « rays are charged with positive electricity, 

 P rays with negative, and both are easily deflected by a magnet, 

 whilst 7 rays show no response to similar stimulus, and are not 

 charged with electricity. In addition to the actual production 01 

 rays, radium, thorium and actinium give out an emanation, although 

 polonium and uranium do not ; this emanation is important, and is 

 a gaseous substance possessing radio-active properties ; it is very 

 unstable, and loses half its activity in four days, and is easily and 

 completely absorbed from the atmosphere by certain substances — 

 e.g., cocoanut charcoal. It is also absorbed by water, and under- 

 ground waters are particularly rich in it. 



a and yS activity may also be created by the impingement of a 

 7 ray on a metallic molecule, and it is found that the intensity of 

 the activity thus evolved varies with the atomic weight of the 

 molecule bombarded. 



Consider now the action of radio-activity on plant and animal 

 life : in general terms this may be stated, that excessive radio- 

 activity totally destroys life, medium radio-activity is irrita- 

 tive and stimulates growth, whilst diminished radio - activity 

 causes no immediate effects, but continued exposure to this 

 attenuated activity causes the cumulative re-action to have 

 effect. This cumulative re-action is mainly effective on the more 

 sensitive highly specialised cells. In fact, the re-action to all forms 

 of radio-activity has a direct relation to the molecular stabihty of 



