26 



DR. F. HORTON ON THE EFFECTS OF CHANGES OF TEMPERATURE 



probable tbat the reason this curve is not a straight line is because the rigidity of 

 the wire is continually increasing. If it were possible to obtain the rigidities at the 

 different temperatures all within a short space of time, it might be expected that a 

 straight line would result. 



In order to give a clearer idea of the rate at which the rigidity is increasing at the 

 various temperatures, a set of curves has been drawn in Diagram III., in which 

 the values of the rigidity modulus are plotted against times at the different 

 temperatures. From these curves it is seen that the rate of increase of rigidity at 



8-IO 



809 



8-08 



'So 

 t 



cj.8-07 

 O 



fl 



3 



8-06 



805 



74-9 



98-05 



05 



97-97 c 



OCX.'- 50 



10 



Time in hours. 

 Diagram III. Showing the alteration of the modulus of rigidity of soft iron with time. 



one temperature is constant, that it is greater the higher the temperature, but that 

 on repeated heatings to the same temperature the rate of increase at that 

 temperature gets less and less, and finally becomes zero. 



From the curve for iron in Diagram I., the value of n at 15 C. was found to be 

 n u = 8-2620 X 10 11 dynes per sij. centim. and the coefficient ft = '0007339. 



