CIECULAR MAGNETISATIONS IN IRON TUBES. 



13 



In the following table, the various dimensional quantities on which the inductions 

 depend are shown for the four tubes : — 



Tube 



2a 



2£ 



log p 2 



p 2 — 1 



1 — r l °gP Z 

 jr — 1 



W/l/ii 



A 

 B 



a 

 b 



3-022 

 3-027 

 3-022 

 3021 



1-031 

 1-050, 

 2-036 

 2-052 



2-1508 



2-1211 



•7898 



•7735 



7-591 

 7315 

 1-203 

 1-168 



•2833 

 •2900 

 •6565 

 •6625 



•7167 

 •7100 

 •3435 

 •3375 



The column headed log p 2 gives the values of 23/Z/n. 



By dividing the numbers in the 33' column by the corresponding numbers in the 35 

 column, we obtain the following ratios of the inductions : — 



E. 



A' /A = -3332 ^ 



B'/B = -33±7 ^ 



M , 

 a' /a = -4349 ^ 



/" 



b'/b ='4363 £- 



where it must be remembered that the ratio ix'\p. is not necessarily the same in all. 

 We also get the following ratios : — 



a/A =-3669 ^1 



b/B =-3647 ^1 

 M 2 



where the suffixes are attached to m to show that the permeabilities for the two kinds of 

 tubes subject to the same axial current are not necessarily the same. 



In the light of these results we shall now discuss Table II. In the first place, it is 

 evident at once that the a tube must differ specifically from the other tubes, being indeed, 

 as already noted, of a different kind of iron. A comparison of the b and B ratios leads 

 to the immediate conclusion that 



fj, for b tube 



fori? tube = ^^33 for axial current "49 amp. 



= •8830 

 = •8800 



1-05 

 2-09 



Now the average magnetic field acting within the substance of the tube is, in terms of 

 the usual theory, 0'212z for the B tube, and 0'159^ for the b tube ; i being measured in 

 amperes. Thus the average fields for the two tubes under influence of the currents given 

 above are 



•104, -223, -445 for the B tube, and 

 •078, -167, -333 for the b tube. 



