810 BELL SYSTEM TECHNICAL JOURNAL 



Compressed Powdered Permalloy — Manufacture and Magnetic Proper- 

 ties.^ W. J. Shackelton and I. G. Barber. The paper gives a brief 

 description of the manufacture of magnetic cores of compressed 

 permalloy powder followed by information co\'ering their magnetic 

 properties with particular reference to their use in loading coils. 

 Production of the powder, and its insulation, pressing and annealing, 

 are discussed. Under magnetic properties, permeability, core loss, and 

 modulation are treated. Curves are given illustrating the character- 

 istics of interest in connection with the design and application of loading 

 coils; and comparisons to corresponding characteristics of compressed 

 powdered iron are made throughout. 



Thermal Agitation of Electric Charge in Conductors.'^ H. Nyquist. 

 The electromotive force due to thermal agitation in conductors is 

 calculated by means of principles in thermodynamics and statistical 

 mechanics. The results obtained agree with results obtained experi- 

 mentally. 



Time-Lag in Magnetization}^ Richard M. Bozorth. An in- 

 vestigation has been made of the time-lag in magnetization in a 

 permalloy wire to determine whether lag can be satisfactorily accounted 

 for as due to eddy-currents alone or whether permalloy shows a marked 

 magnetic viscosity such as has been observed by Ewing in iron wires. 

 Eddy-current lag has been calculated approximately in a manner which 

 takes into account the changing slope of the magnetization curve. A 

 comparison of the calculated and observed magnetization-z;5.-time 

 curves indicates that the effect is well accounted for as eddy-current lag 

 alone. The eddy-current lag has also been calculated for an iron ring, 

 for which the time-lag has been reported recently in a number of papers 

 by Lapp. The time-lag which he observed is satisfactorily accounted 

 for as eddy-current lag instead of as magnetic viscosity as he had 

 supposed. 



Thermal Agitation of Electricity in Conductors}^ J. B. Johnson. 

 Statistical fluctuation of electric charge exists in all conductors, 

 producing random variation of potential between the ends of the con- 

 ductor. The effect of these fluctuations has been measured by a 

 vacuum tube amplifier and thermocouple, and can be expressed by the 

 formula P = {2kT/T)J]^R(o)) \ F(co) \-dco. I is the observed current in 

 the thermocouple, k is Boltzmann's gas constant, T is the absolute 



8 Jourtial of the A. L E. E., Vol. XLII, No. 6, pp. 437-440, June, 1928. 



9 Physical Review, Vol. 32, No. 1, pp. 110-113, July, 1928. 

 ^^ Physical Review, Vol. 32, No. 1, pp. 124-132, July, 1928. 

 ^^ Physical Review, Vol. 32, No. 1, pp. 97-109, July, 1928. 



