July 1, 1921] 



SCIENCE 



nently and effectively cured, so that this kind 

 of treatment has already been of sufficient use 

 in therapy so that all who are familiar with it 

 are at one in believing that it is highly desir- 

 able to introduce in all large centers of pop- 

 ulation these radium and X-ray hospitals of 

 the kind which exist in Boston, New York, 

 Chicago, Buffalo, Los Angeles, and several 

 other cities, and which Paris is now to have 

 because of the gift which you are making to 

 Madame Curie. 



The electroscope which by looking at the in- 

 verted image upon the screen you now see 

 discharging rapidly under the influence of 

 the gamma rays from the radium, is exposed 

 only to the rays which have passed through 

 more than a half inch of lead; for the ra- 

 dium is completely enclosed in lead walls 

 of that thickness. This gives you some 

 idea of the marvelous penetrating power of 

 these gamma rays. I now wish to show you 

 some of Dr. C. T. R. Wilson's photographs of 

 the actual tracks of the alpha, beta and gamma 

 rays through air. After seeing these straight 

 line tracks of the alpha and beta rays you 

 will not doubt that radium is actually shoot- 

 ing off big and little projectiles of the kind I 

 told you about. The wiggly, snaky tracks 

 due to the gamma and X-rays are perhaps 

 even more interesting and enable you to visu- 

 alize somewhat what goes on in your body 

 when you are taking X-ray treatment. Can 

 you now wonder that these rays tend to destroy 

 the tissues and to produce burns? ( 



Now a word as to the significance of this 

 radio-active process. The therapeutic signifi- 

 cance I have already referred to, but from my 

 point of view the insight which radium gives 

 into the nature of matter is of vastly more im- 

 portance than any possible effeets it has in the 

 cure of disease or in the alleviation of pain. 

 Twenty-five years ago if we had been told that 

 any kind of matter possessed the property of 

 throwing out projectiles with these enormous 

 speeds we would have said " impossible." But 

 not only in the enormity of the speeds of these 

 projectiles is radium astonishing and revolu- 

 tionary. There is something sublime about its 

 ceaseless, unaltering and apparently unalter- 



able activity, its complete indifferesce to in- 

 tense heat or to extreme cold, to electrical or to 

 chemical treatment of any kind. It is a 

 property of the atom itself which we can not 

 at present control in any way. 



But the third effect of this discovery is 

 more important still, for what does it show 

 that matter is doing? These alpha particles 

 which are being shot off are portions of the 

 atom of uranium or of the atom of radium 

 and the thing which is left after the ejection of 

 the alpha particle from an atom of uranium 

 is no longer uranium. Its chemical and phys- 

 ical properties have entirely changed. The 

 uranium atom in shooting off one of these 

 alpha particles is thereby transmuting itself 

 into another element. When it has shot off 

 three alpha particles it has transmuted itself 

 into radium, and when it has shot off five more 

 it has transmuted itself into lead. We have 

 seen in the laboratory the growth of lead out 

 of uranium, and have followed the whole chain 

 of transmutation of elements through this 

 radio-active process. This necessitates a con- 

 ception of the nature of matter which was ab- 

 solutely foreign to our thinking in the nine- 

 teeenth century, and it is revolutionary in its 

 significance. It means that these " eternal " 

 elements — this radium and this uranium which 

 we have here — are not eternal at all. The 

 average life of the atoms of this radium is 

 just 2,500 years, and after that time the aver- 

 age atom will have disappeared as radium, 

 and if the world's supply of radium has not 

 then mostly disappeared it will be because 

 new radium is being produced all the time 

 out of uranium. But uranium is the heaviest 

 element we know of, and what is happening 

 to it? It too is disappearing. But whence 

 came it ? It is true that the average fife of the 

 uranium atom is approximately eight billion 

 years, so that when you go back so far as 

 that, you may be inclined to say that it doesn't 

 make much difference to this particular Re- 

 publican administration where it did come 

 from. Ah, but wait! In your thinking you 

 have been forced to admit for the first time 

 in history not only the possibility but the 

 fact of the growth and decay of the elements 



