102 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



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\ATf) 



Fig. 13 — Pull charafteristics for approaching saturation. 



The dashed tangent Hnes give values of F', so corresponding vahies of 

 F' and F ran be read for various values of 5. Values of F' /F for the 

 results of Fig. 11 have been thus determined, and are plotted in Fig. 13 

 against (fl/4x)" for the values of x applying to the individual ('ur\"es of 

 Fig. 11. 



The values of F' /'F thus plotted determine a family of straight lines 

 having a common intercept at the origin of ??". In this respect these re- 

 sults are representative of the pull characteristics of electromagnets 

 when plotted in this way. As an empirical fact, apart from any analysis, 

 this linearity pro\'ides a useful method of plotting pull observations in 

 the high density region, as it facilitates interpolation and the detection 

 of inconsistent observations. 



The observed linearity in the relation between F' IF and 3^" conforms 

 to the relations postulated in (15) and (17), of which the former should 

 apply for core saturation. If (15) applies, the common intercept of 0.65 

 at 5" = in Fig. 13 should equal 1 — {ip' /ip")', indicating a value for 

 (/?' V" ('f 0.5!). To determine if the relation fully conforms to (15), the 

 relation between the slopes of the lines and the corresponding \-alues of 

 X must be compared with that indicated by this equation. 



Let //" })e the observed slope of the plot of F' /F versus 5" for a particu- 



