54 



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



corresponding temperatures, and in every case the resulting curve was a straight line. 

 Tliu lengths of tin- wires at C. were found l>v exterpolation and the values of the 

 coefficients of expansion calculated. In order to show the accuracy obtained, the 

 lengths of the wires at the different temperatures were calculated from the formula 

 /, = (1 -{- at), where 1^ and l t are the length of the wire at C. and t C. respec- 

 tively and a is the coefficient of expansion. It is peculiar that in several cases the 

 difference between the observed and calculated values was far larger at the ordinary 

 laboratory temperature than at any other. 



Below are given the complete set of observations on the finst wire tested, viz. , soft 

 iron. For the other metals I give merely the value found for the coefficient of 

 expansion and the average difference between the observed and calculated lengths at 

 the various temperatures. 



TABLE XII. Soft Iron. 



For the observations recorded in Table XII. the coefficient of expansion for soft iron 

 is -00001118. Another determination gave a ='00001111. The mean of these. 

 a = -000011145, is the value used to correct the observed periods of oscillation in the 

 determination of the temperature coefficient of the rigidity modulus. 



The coefficients of expansion of the other wires experimented on and also of the 

 gun-metal bar already referred to are contained in Table XIII. 



