174 



Dr. M. Maclean. On the Effects of 



materials. By putting weights into the scale pan, and taking them 

 out, and noting the readings of the pointer on the scale, the temporary 

 and permanent elongation in the wire for different weights were found. 

 The numbers are given in the second and third columns of Tables V 

 to XIY. The currents in the fourth columns are calculated from the 

 deflections of the galvanometer when the stated weights are on the 

 wire, and the thermo-electric differences in the fifth column are found 

 by multiplying the currents in the fourth column by the total resistance 

 in the circuit in each case. 



§ 18. The numbers in the tables are plotted in curves with percentage 

 permanent elongation as abscissae, and thermo-electric differences as 

 ordinates. The thermo-electric difference between free platinoid and 

 strained platinoid, rises rapidly with the permanent elongation of the 

 strained wire. For manganin and lead, both commercial and pure, it is 

 very nearly constant up to a permanent elongation of i per cent. 



Mr. Alexander Wood, Thomson Experimental Scholar in the Physical 

 Laboratory, The University, Glasgow, has rendered valuable help in 

 the experimental work and in the calculations. 



Table V. — Electrotype Copper. 



Current from Stretched to Unstretched. 



Temperature difference = 87° C. Total resistance in circuit 

 = 15-56 ohms. 



Total weight 

 in grammes. 



Percentage 

 temporary 

 elongation. 



Percentage 

 permanent 

 elongation. 



Current in 

 mikroampere 

 per degree 

 with, weight on. 



Thermo-electric 

 difference in 

 mikrovolt 

 per degree. 



250 



0-06 





0-00020 



0-00311 



500 



0-1 





0-000267 



0-00415 



750 



0-137 





-000567 



-00882 



1000 



0-18 



0*-036 



0-000934 



-01452 



1250 



0-21 



0-057 



-001200 



0-01867 



1500 



0-264 



0-072 



-00137 



-02127 



1750 



0-318 



0-104 



-001866 



-02905 



2000 



0-348 



0-144 



0-002 



03113 



