miller: resistance and inductance of wires 455 



The chief merits of the device when compared with other 

 methods of characteristic evaluation seem to be its simpUcity and 

 precision, and the saving of time resulting from its use. Sohitions 

 are made directly, without reference to normal wpc, voltage 

 ratios, exponents, etc. These considerations should recommend 

 it to testing and standardizing laboratories. 



PHYSICS. — The effective resistance and inductance of iron and 

 bimetallic loires.^ John M. Miller, Bureau of Standards. 



When a current of electricity flows through an iron wire, the 

 lines of magnetic force and the resulting magnetization of the 

 iron are circular. From measurements of the self-inductance 

 of the wire with direct current an exact permeability curve for 

 circular magnetization can be obtained. As ordinarily measured, 

 the permeability for axial magnetization is obtained. A compari- 

 son of the two kinds of magnetization shows that for some wires 

 the permeability curves are similar, but that for others the 

 circular permeability may be considerably less than the axial. 

 The differences are due probably to lack of homogeneity or iso- 

 tropy of the iron caused by drawing and by heat treatment. 



A method based upon Anderson's modification of the Max- 

 well bridge for measuring inductances is used to measure the 

 effective resistance and inductance of six samples of iron tele- 

 graph and telephone wires and three samples of copper-clad steel, 

 bimetallic wires. The measurements are made at frequencies 

 up to 3000 cycles per second and with currents up to 10 amperes. 

 The results are given by tables and curves. The so-called Steel 

 telephone wires are considerably poorer conductors at low 

 frequencies and low current strengths than the grade called 

 ''Extra Best Best, " but at higher frequencies and current strength 

 the Steel wires may be better conductors. At the higher fre- 

 quencies the resistance and inductance of the copper-clad wires 

 become practically independent of the current flowing through 

 the wire. 



^ Detailed paper to appear in the Bulletin of the Bureau of Standards. 



