Brown — Note on the Change of Length in Niclcel Wire. 301 



contraction for the corresponding direct magnetic field, that is, the A. C. 

 contraction is about 161 times the D. C. contraction with the smallest load 

 on, 1'58 times for the middle load, and 1'49 times for the greatest load. 

 Again, if we were to plot the A.C. contraction as ordinates, and the corre- 

 sponding values of the maximum alternating fields as abseissse, the multiplying 

 factors would be 1'56, 1"50, and 1'37 respectively, in the order of the loads 

 from the low to the high. 



For assistance in reading the microscope I am indebted to the Rev. Br. 

 P. V. Ryan, a third-j'ear student in Physics of this College. 



SOIFNT, PEOf!. E.D.S., VOL. XIV, NO. XXT. 3 B 



