410 



Prof. D. E. Hughes. 



[Mar. 6, 



am forced to give roughly the general outlines, as in fig. 1. Suppose 

 we take a compound bar of iron, of eleven strips, and draw it over a 

 permanent magnet, polarising its lower side only, its neutrality may 

 be found nearly perfect, or 15° of remaining north polarity at the 

 north end ; now on carefully separating these rods and observing the 

 same ends, we have for the lower or the side which had been 



magnetised, 350° north; the following successively observed would 

 give 10° south, 35° S., 55° S., 60° S., 50° S., 40° S., 22° S., 10° S., 6° S., 

 5°S. ; here all the superposed bars are opposite in polarity to the 

 exterior 350° north, the total south observed being 292, plus 30° south 

 obtained from the exterior, by the coating of its lower face with the 

 milim. of iron strip already mentioned. We are thus enabled to 

 account for 323° degrees south, and 350° north, leaving a remaining 

 magnetism unaccounted for of 12°, which was doubtless disseminated 

 on the surface of each bar on separation. 



The above curves were obtained from the same polar (north) end of 

 a compound bar of iron, the south or opposite end of the bar would 

 give reversed curves to these. The curves are reductions to a similar 

 force, but do not exhibit the perfection of the curves obtained on a 

 larger scale. 



No. 1 represents the typical curve of penetration of a bar of iron, 

 whilst under the influence of an exterior polarising force, applied at A, 

 or only at one side of a bar. When the force is applied to the whole 

 of the exterior surface (as in a coil), A would represent the polar 

 force on its surface, whilst B the interior. In all cases there would 

 be a depression at the centre; great if the bar is thick, and com- 

 paratively small if the bar is thin. The curve rises with the exterior 

 polarisation force, but in no case can a reversal ensue whilst under its 

 influence. The instant, however, that it ceases, the higher magnetic 

 power of the exterior layers reacts gradually and successively upon the 

 weaker interior layers, rotating them through neutrality to a strong 

 opposite polarity. 



