286 



TABLES 296, 297. 

 PERMEABILITY OF IRON. 



TABLE 296. Permeability of Iron Rings and Wire. 



This table gives, for a few specimens of iron, the magnetic induction B, and permeability /*, corresponding to th 

 magneto-motive forces H recorded in the first column. The first specimen is taken from a paper by Rowland,* 

 and refers to a welded and annealed ring of "Burden's Best " wrought iron. The ring was 6.77 cms. in mean 

 diameter, and the bar had a cross sectional area of 0.916 sq. cms. Specimens 2-4 are taken from a paper by 

 Bosanquet,t and also refers to soft iron rings. The mean diameters were 21.5, 22.1, and 22.725 cms., and the 

 thickness of the bars 2.535, 1.295, an ^ -7544 cms. respectively. These experiments were intended to illustrate the 

 effect of thickness of bar on the induction. Specimen 5 is from Ewing's book,$ and refers to one of his own 

 experiments on a soft iron wire .077 cms. diameter and 30.5 cms. long. 



TABLE 297. -Permeability of Transformer Iron. 



This table contains the results of some experiments on transformers of the Westinghpuse and Thomson-Houston 

 types. Referring to the headings of the different columns, Mis the total magneto-motive force applied to the iron ; 

 M '/ 1 the magneto-motive force per centimetre length of the iron circuit ; B the total induction through the mag- 

 netizing coil ; B / a the induction per square centimetre of the mean section of the iron core ; M / B the magnetic 

 reluctance of the iron circuit; Bl/Ma the permeability of the iron, a being taken as the mean cross section of the 

 iron circuit as it exists in the transformer, which is thus slightly greater than the actual cross section of the iron. 



SMITHSONIAN TABLES. 



* " Phil. Mag." 4 th series, vol. xlv. p. 151. 



t Ibid, sth series, vol. xix. p. 73. 



J " Magnetic Induction in Iron and Other Metals," 



T. Gray, from special experiments. 



