﻿Simple Model to Illustrate Elastic Hysteresis. 511 



value obtained is A = 0*94 x 10 ~ 15 cm. 2 , which may be subject 

 to an experimental error oil 2 or 3 per cent. It is difficult to 

 estimate the degree of: precision with which this figure 

 represents the real dimensions of the molecule. The mea- 

 surements of viscosity, owing to the comparatively small 

 temperature range over which they extend, provide no proof 

 that, for this gas, Sutherland's law holds. Indeed, as men- 

 tioned earlier, it is improbable that the sulphur dioxide in 

 the circumstances of the experiments was sufficiently super- 

 heated to give the true value of Sutherland's constant. It is 

 not unlikely that the actual mean collision area differs from 

 that calculated by an amount appreciably greater than that 

 attributable to experimental error. 



Summary of Results. 

 Table II. 



Viscosity in C.G-.S. units X 10~ 4 . 



Sutherland's 

 constant. 



Mean col- 

 lision area 

 (cm.'xlO- 15 ). 



18°'0C. 



ioo°-o C. 



o°-o 0. 



1-253 



1-630 



1-168 



416 



0-94 



In conclusion, the author would like to record his apprecia- 

 tion of the continued help and advice received from Professor 

 Rankine, and also to thank the Goverment Grant Committee 

 of the Royal Society for a grant which enabled the research 

 to be undertaken. 



Imperial College of Science 



and Technology, London, S.W.7. 

 10th June, 1922. 



XL VIII. On a Simple Model to Illustrate Elastic Hysteresis. 

 By S. Lees, M.A., St. Johns College, Cambridge*. 



§ 1. Introduction. 



MUCH material has accumulated f in recent years con- 

 cerning the behaviour of metals when taken through 

 either a series of cycles of alternate compressions and 

 tensions, or a series of periodic shear stresses. In the 

 main, the experimental results here utilized are those of 



* Communicated by the Author. 



t See e. g. 'Dictionary of Applied Physics,' vol. i. p. 178. 



