﻿254 



Dr. J. A. Ewing on the 

 Table II. 



Range of 

 a Particles. 



Product. 



Eange of 

 a Particles. 



I 

 Product. 



4-8 cms 



5-50 „ 



5-8 „ 



6'55 „ 



Eadioactinium. 

 Actinium B. 

 Emanation. 

 Actinium X. 



3-9 cms 



5-0 „ 



5-5 „ 



5-7 „ 



8-6 „ 



Eadiotborium. 

 Thorium B. 

 Emanation. 

 Thorium X. 



Thorium 0. 



: 



It is seen that ^ach of the products of thorium and actinium 

 occupies a corresponding place in the table, the only differ- 

 ence being that there is no product in actinium corresponding 

 to thorium in thorium. 



The similarity in the number and nature o£ the products 

 of these two elements has often been pointed out, and the 

 relationship described above is probably more than a coinci- 

 dence, and indicates that there is a close connexion in the 

 mode of transformation of the atoms of thorium and actinium. 



In conclusion I again wish to express my best thanks to 

 Professor Rutherford for his usual interest he took in this 

 work, and for the kind advice I received from him. 



The Macdonald Physics Building, 

 Montreal, June 10th, 1906. 



XXXIII. The Molecular Structure of Metals. 

 By J. A. Ewing, LL.D., F.R.S., MJnst.CE* 



I INTEND to devote this Address to considering in certain 

 aspects the inner structure of metals and the manner in 

 which they yield under strain. It will not be disputed thas 

 this is a primary concern of the engineer, who in all his 

 problems of design is confronted by the limitations imposed 

 on him by the strength and elasticity of the materials he 

 employs. It is a leading aim with him to secure lightness 

 and cheapness by giving to the parts such dimensions as are 

 no larger than will secure safety; and hence it is of the first 

 importance to know in each particular case how high a stress 

 may be applied without risk of rupture or of permanent 



* Communicated by the Author, being 1 the Presidential Address to the 

 Engineering Section of the British Association for the Advancement of 

 Science, York, 1906. 



