ABSTRACTS OF TECHNICAL ARTICLES 725 



Magnetic Hysteresis at Low Flux Densities.* W. B. Ellwood. 

 The energy loss per cycle in a ferromagnetic material subjected to small 

 alternating fields is sometimes separated into three parts: the first 

 due to eddy current loss, the second to hysteresis presumed to follow 

 Rayleigh's laws at these flux densities; the origin of the remainder is 

 unknown and is the subject of much controversy; it has been variously 

 termed "magnetic viscosity," "after effect," and "square law hystere- 

 sis." In studying energy loss in a ring of compressed iron dust, 

 hysteresis loops have been measured ballistically by a new method with 

 a relative error in Bm as low as 0.01 per cent. The range in maximum 

 flux density is from 2 to 100 gauss. The loops are lenticular and very 

 slender, B^ being about 1500 times the remanence for the smallest 

 loop. The smaller loops are at flux densities considerably below those 

 investigated by Rayleigh. His findings as to variation of area, of 

 remanence, and of permeability with loop amplitude are confirmed and 

 extended through the new range of flux densities, though the shape of 

 the loops is not as simple as that he proposed. The energy loss per 

 cycle is proportional to Bm^ while the remanence is proportional to 

 Bm''- The ballistic measurements have been compared with a-c. 

 bridge measurements on the same specimen. The loss of unknown 

 origin is not included in the hysteresis loss measured ballistically. 

 Comparison is made between the third harmonic induced voltage com- 

 puted by a Fourier series analysis of the ballistic loops and the har- 

 monic actually generated by the specimen. Agreement is found be- 

 tween the measured and the computed values. Possible explanations 

 of the discrepancy between the ballistic observed energy losses and 

 a-c. findings are discussed. 



A Fugue in Cycles and Bels.^ John Mills. Engineers who are 

 questioned by their musical acquaintances about electrical transmis- 

 sion and what it is likely to do to the art are likely to find an explana- 

 tion, even in the simplest of terms, shooting over the heads of their 

 audience. The reason lies not in the inherent difficulty of the concepts, 

 but in their number, which exceeds the power of memory to retain as 

 unrelated facts. In this volume John Mills has strung his facts to- 

 gether on the thread of logical relationship, but he has tied them into 

 his readers' existing knowledge by many a deft touch of anecdote or 

 humor. Frequency, with its relation to harmony and discord, opens 

 the volume; there follows a physical picture of vibrations in various 

 media and how one form is transformed into another. Pitch and 

 intensity are next considered. An entire section is devoted to tele- 



" Physics, July, 1935. 



* Published by D. Van Nostrand Company, Inc., New York, N. Y., 1935. 



