THE RADIO-ACTIVE POINT OF VIEW. 

 By WILLIAM DUANE. 



In estimating the age of the earth one should measure the time 

 that has elapsed by some process in nature that takes place in one 

 direction only and that does not change its rate when conditions 

 (temperature, pressure, etc.,) alter. In most of the estimates of 

 geological periods of time that have been made, the " clocks " em- 

 ployed do not fulfill these conditions. Estimates based on the tem- 

 perature of the earth, or of the sun, for instance, cannot be reliable, 

 for the temperature of a body may fall or it may rise. Further, the 

 rate of change of the temperature depends upon a variety of condi- 

 tions, such as the amount of energy radiated, the supply of energy 

 to it, etc. 



Attempts have been made to deduce the age of certain minerals 

 from the appearance of little round marks in them, called haloes. 

 These haloes are supposed to be due to radiation from minute specks 

 of radio-active matter at their centers. The colors produced by 

 radiation in transparent substances depend, to a considerable extent, 

 upon the temperature, so that no very great weight can be put upon 

 geological periods of time estimated by means of haloes. 



There are, however, other radio-active processes, the rates of 

 which do not, so far as we know, depend on the temperature or the 

 pressure, nor upon any other physical or chemical state. 



During the last twenty-five years a large number of radio-active 

 transformations of one chemical element into another have been dis- 

 covered. Students of the subject agree that these transformations 

 take place in one direction only, i.e., from an element of higher 

 atomic weight to an element of lower atomic weight. Further, no- 

 body has been able to alter the rate of a radio-active transformation 

 by any process whatsoever, although numerous attempts have been 

 made to do so. These radio-active changes, therefore, seem to offer 

 a reliable means of estimating certain periods of time. 



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