Radioactivity — ^Artificial and Natural ^ 



By KARL K. DARROW 



"O ADIOACTIVITY Is a world-famous word relating to a world- 

 -^^ famous subject. In general, when a statement of this sort is 

 spoken, it is more than likely to be foolish ; for specialists are altogether 

 too addicted to imagining that their special interests are of world-wide 

 concern when perhaps not fifty thousand people have even heard of 

 them. With respect to radioactivity, though, the statement is correct. 

 It would have been difficult indeed for any literate person to miss 

 making the acquaintance of this word, in any year since 1900. I 

 might say that radioactivity has been the best-advertised topic in 

 modern physics — and this is not to say that it has been over-advertised ! 

 It is in fact the only part of modern physics which has received some- 

 thing approaching its due renown. Such good fortune cannot of course 

 be altogether due to the fundamental values of the subject. A great 

 part of the fame of radioactivity comes from medical applications and 

 even more from medical hopes, and some from incidental things, such 

 as the tragic end of one of its great students and the sex of two others. 

 Still it is a matter for rejoicing that whatever the reasons may be, one 

 portion of physics now enjoys its proper quota of the glory to which 

 so many others are entitled. 



The discovery of radioactivity took place in 1896. Quite a number 

 of things of the highest importance to physics — and to humanity at 

 large — were begun between 1895 and 1900, and of these the study of 

 radioactivity was the second. The study of X-rays was the first. The 

 second was commenced only because the first had been, and therefore 

 I speak of the first. Imagine a tube containing air and a couple of 

 electrodes a few inches apart, and suppose that you have a battery 

 which can supply a durable current at ten thousand volts or more, and 

 an air pump as well. If the air is at atmospheric pressure, the ten 

 thousand volts can be applied between the electrodes and nothing will 

 happen. If with the pump you now reduce the pressure of the air to 

 about a thousandth of the atmospheric value, the air which remains 

 in the tube will become very luminous and splendid. If next you re- 



1 A lecture sponsored by the New York Electrical Society and by the American 

 Institute of Electrical Engineers. Delivered before the former on January 12, 1938. 

 Scheduled for presentation to the latter at its Northeastern District Meeting in 

 Lenox, Massachusetts, on May 19, 1938. 



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