THE PROBLEM OF RADIOACTIVE LEAD. 1 



By Theodore W. Richards, Harvard University. 



We meet to-day with happiness which six months ago would have 

 seemed beyond the bounds of reasonable hope. After anxious months, 

 the confidently awaited victory, which last spring still seemed far 

 away, has croAvned the cause of justice, truth, and liberty. We in 

 America rejoice that this cause is our cause, and that at the most 

 critical time we were a'ble to render effective help to the staunch and 

 brave allied forces which had fought so long and so nobly. 



The object of this address is not, however, to appraise the military 

 issues of the great war so fortunately ending, nor to deal with the 

 weighty international problems now faced by the world, but rather 

 to bring before you other considerations, having to do with the ad- 

 vancement of science. 



The particular subject chosen, namely, the problem of radioactive 

 lead, is one of peculiar and extraordinary interest, because it in- 

 volves a readjustment and enlargement of many rather firmly fixed 

 ideas concerning the chemical elements and their mutual relations, 

 as well as the nature of atoms. 



Within the last twenty years the definition of these two words, 

 " elements " and " atoms," has been rendered somewhat uncertain and 

 bids fair to suffer even further change. Both of them are ancient 

 words, and both even a century since had acquired meanings different 

 from those of long ago. Thales thought of but one element, and 

 Aristotle's elements — earth, air, fire, water, and the quintessence, 

 derived perhaps from yet more ancient philosophy — were not plenti- 

 ful enough to account for all the manifold phenomena of nature. 

 Democritus's old idea of the atom was associated rather witli the 

 philosophical conception of indivisibility than with the idea of chem- 

 ical combination in definite proportions. To-day many chemists and 

 physicists think that the chemical atoms of the last century are no 

 longer to be considered as indivisible. In that case, the old Greek 

 name " atom " is no longer fitting, because it denotes indivisibility. 

 Some one has even facetiously suggested that the word " torn " — 

 indicating divisibility — would be more appropriate. Moreover, if 



1 Address of tie president of the American Association for the Advancement of Science, 

 Baltimore, December, 1918. Reprinted by permission from Science, N. S., Vol. XLIX, No. 

 1253, pp. 1-11, Jan. 3, 1919. 



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