﻿200 Messrs. Hawthorne and Morton on Deflexions 



ratio may be estimated at 16 to 1, so that the a rays of the 

 emanation produce about 2 to 7 ions per c.c. per second. 



6. The penetrating radiation, observed by H. L. Cooke in 

 a closed brass vessel, produced about 4*5 ions per c.c. per 

 second. This cannot be attributed to the active matter in 

 the atmosphere, but the radium present in the earth^s crust 

 appears to be of the right order to account for it. 



7. About 1*8 X 10 -11 grains of radium bromide is the 

 estimated equivalent o£ the active matter per c.c. present in 

 the earth's crust sufficient to account for the penetrating 

 radiation. This appears to be about four times as large as 

 the average amount found by Strutt by direct observation 

 of rock specimens. 



8. The ionization in the atmosphere is due partly to pene- 

 trating radiation from active matter in the earth, partly to 

 a radiation from the emanation in the atmosphere. 



I am most grateful to Professor Rutherford for his 

 assistance in difficulties and for valuable suggestions in 

 experimental work and theoretical considerations. 



Montreal, June 1906. 



XXVIII. Supplementary Note on the Deflexions caused by 



a Break in an Overhead Wire carried on Poles. By 



\ V W. Hawthorne, B.A., B.E., and W. B. Morton, M.A* 



TN a paper published in the May number of this Magazine 

 . \ JL we gave an investigation of this question in which the 

 wires were treated as inextensible. It is not difficult to 

 modify the work so as to take into account the elastic stretch 

 accompanying increase of tension. This is the object of the 

 present note, in which, as in the former case, numerical values 

 are worked out, so as to get an idea of the importance of this 

 element in actual cases. 



The notation of the former paper is retained, and in addition 

 we use \ to indicate the elastic modulus of the wire, i. e. 

 increase of stretching force divided by fractional increase of 

 length. Thus we have 



s 



and, in order to take account of the change of 10 caused by 

 extension, we write 



T w 



±—wc= — c, 



s 



* Communicated by the Authors. 



