SYMPOSIUM OX RADIOACTIVITY. 43 



I. PHYSICAL PROPERTIES OF R,\DIUM. 



By Henry Crew, 



Northwestern University. Evanston. 



When the President of this Academy invited me. or rather 

 commanded me — for an invitation implies the opportunity.' of 

 sending one's regrets, and this opportunity I did not have — I say, 

 when the President of this Academy commanded me to say some- 

 thing concerning the physical properties of radium, he was 

 courteous enough and clever enough to add that no special knowl- 

 edge of the subject was needed for participation in this sympxD- 

 sium; and said that the smaller the amount of one's first-hand 

 information, the better prepared he would be to give the desired 

 "editorial point of view." So that explains why I am here 

 instead of Professor McCoy or Professor Millikan, or some other 

 man who has furnished real contributions to knowledge on this 

 subject, and who has thereby acquired that splendid perspective 

 in science which is obtained only from one's own individual re- 

 search, a fact with which no one here is better acquainted than 

 our distinguished president. 



If any one ever dreamed of any sharp boundary- between the 

 various physical sciences, the rise of physical chemistry, the more 

 recent developments of dynamical geology- and astro-physics, the 

 entire history of radio-activity, and the award of the Nobel pri^ 

 in chemistn.' to the Professor of Physics at the University of 

 Manchester, must certainly have dispelled the illusion. At the 

 same time, there is a general and valid distinction between those 

 properties which we call physical and those which we denote as 

 chemical. This distinction rests upon the definition of physics 

 as the science which deals with three groups of "over-individual 

 objects,'' namely, ether, electrons and matter, except in so far 

 as changes of composition are involved. I shall tr}- to confine 

 myself, therefore, to such properties of radium as may be called 

 "physical," in this narrow sense of the term. 



If the discovery of a new substance were reported today, some 

 of the most fundamental questions which might be asked con- 

 cerning its physical properties are : 



(i) Has it weight and inertia, and do these bear to one another 

 the same constant proportion as in ordinary matter? 



