CIRCULAR MAGNETISATIONS IN IRON TUBES. 



Table I. 



Showing the relation between the average magnetic induction (33) in an iron tube 

 under the influence of an axial current, and the average magnetic force (h) as it would be 

 throughout the region occupied by the iron if the iron were replaced by a substance of 

 unit permeability. 



h 



33 



M = S3/h 



h 



33 



/u = 53/b 



•0299 



9-2 



307-9 



1-654 



2251 



1361 



•0475 



14-6 



308-8 



2-068 



3612 



1747 



•0572 



18-6 



326-2 



2-481 



4900 



1975 



•0724 



25-1 



347-2 



2-895 



5688 



1965 



■1046 



39-2 



375-2 



3-308 



6391 



1932 



•1234 



47-8 



387-5 



3-722 



6967 



1872 



•1900 



79-6 



419-2 



4-136 



7377 



1784 



•2157 



949 



440-3 



4-570 



7823 



1720 



•3218 



162-8 



505-7 



4-963 



8276 



1668 



•4136 



213-4 



516-2 



5-377 



8692 



1617 



•4626 



249-0 



538-6 



5-790 



9054 



1564 



•8270 



544-2 



658-0 



6-204 



9452 



1524 



•8493 



577-9 



680-5 



6-617 



9825 



1485 



•241 



1266 



1021 









It should be mentioned that in the tube used, A namely, one ampere of axial current 

 corresponds to an average magnetic field of 0*2150. Thus the highest magnetic field 

 corresponds to an axial current of fully 30 amperes. In the experiment this highest 

 value was attained by using a multiple wire of many insulated strands, and passing a 

 moderate current through all in series. 



It is important to notice that with a current of one ampere the field at the internal 

 surface of the tube is nearly 0'4 ; and similarly in any case the maximum field acting on 

 the iron is about 1*8 times the estimated average field acting over the entire radial 

 section. 



The relations existing between the quantities tabulated above are shown graphically 

 in the Plate. The induction curve and permeability curve are both shown complete, and 

 on a large enough scale to bring out the deviations from smoothness. They are drawn 

 through all the points. 



The induction curve is very similar in form to the induction curves obtained when an 

 iron rod is longitudinally magnetised. The same may be said in a general way of the 

 permeability curve. One particular, however, in which the results differ appreciably 

 from results obtained for iron rods and anchor rings is in the comparative values of the 

 maximum permeability and the permeability for the smallest field. This smallest 

 permeability is remarkably high as compared with the initial permeabilities given, for 

 example, by Rowland, Ewing, or Lord Rayleigh. On the other hand, the maximum per- 

 meability is comparatively small, falling short of 2000. How far this may be due to the 

 form of the iron tube, or to the inaccuracy of the estimate of the average magnetic force, 



