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.-IBSTRACrS ()/• lECllXIC.Il. r.-ll'ILRS 5.'7 



first the i;i'iu'r.il [)r<)|XTtics of ferrninaRiielic IkkIjcs and tliu particular 

 lorins of mai;in'tization ciir\'es and hystert'sis loops cxhihili-d hy ircn, 

 I nhalt, nirkfl, and thoir alloys with i-arh othiT and with other elements. 

 The Heusler alloys are also described. The elTects of temperature 

 u(>on magnetization are then fliscus.sed in detail for the case of iron 

 and the behavior of alloys is compared with this as a standard, both 

 reversible and irreversible ch.mges being discussed in some cases. 

 The transient effects of mechanical strains within the elastic limit 

 and the permanent effects of o\-er-strain of the kinds usually met 

 with in practice are considered. The re\'iew concludes with sjx-cula- 

 tions in regard to the electronic groups in the atomic structure which 

 are responsible for the occurrence of ferromagnetic properties. One 

 hundretl and forty references to recent periodical literature are in- 

 tenditl to give starting points for more detailed study of any of the 

 subjects discussed. 



Permeater for Alternating Current Measurements at Small Ma'^net- 

 izinii Forees.' C A. Kei.I.s.m.i.. This is a description of a permea- 

 meter for making alternating current measurements of permealiility 

 on toroidal specimens at small magnetizing forces and at telephonic 

 frequencies. It is a special type of transformer with a single turn 

 secondar\-. The primary consists of a suitable number of turns of 

 insulated copper wire wound directly on a finely divided toroidal 

 magnetic core made of one of the high permeability permalloys. 

 The single turn secondary is an annular copper shell enclosing the 

 priman,- with an additional space provided for the core to be tested. 

 The copper shell is provided with con\enient means for opening and 

 closing. The sample whose permeability is to be determined is inter- 

 linked with the open secondary- which is then closed. The inductance 

 of the instrument connected as one arm of an inductance bridge is 

 then measured at the primary terminals. From the value thus ob- 

 tained, the constants of the transformer and the diniensioiis of the 

 sample, the permeability is computed. 



Furnace Permeater for Alternating Current Measurements at Small 

 Maanelizinn Forces? G. A. Kells.vli,. This is an adaptation of the 

 permeamcter previously described for the measurement of permeabil- 

 ity at elevated temperatures. It consists essentially of a permeameter 

 with an addition of an annular electric furnace immediately surround- 

 ing the sample under test and suitably heat insulated from the other 

 parts of the instrument. Like the simpler permeameter, it measures 

 the permeability of ring samples for sm dl mignetizing forces at 



•JOS. A. and R. S. I., 8, pp. 329-.?.?.S, 1024. 

 'J. O. S. A. and R. S. I., 8, pp. 669-674. 1024. 



