400 The Villari Critical Points of Nickel and Iron. 



identical with that on unloading. With nickel the curve lies 

 entirely below the load-line and never cuts the line. 



In figures 4 and 5 the curves are described as having been 

 obtained with a magnetizing force of 003 C.G.S. units ; 

 but other experiments showed almost precisely the same 

 curves to be obtained for any force between 0'03 and 0*3 

 C.G.S. units. Between these limits of force the whole of the 

 magnetization is practically temporary provided the wires 

 have been stretched to the extent these were. 



From what has been said and from the figures it is easy to 

 see what would be the general character of the curves, show- 

 ing the relation between change of temporary permeability 

 and change of load for any magnetizing force whatever. If 

 a piece of iron wire be tested with loads nearly up to the 

 breaking-point, then for magnetizing forces ranging from 

 to somewhere about *3 C.G.S. units the curves will be identi- 

 cal with those of fig. 4, and will not cut the load-line. For a 

 value of force above *3 the curves will cease to be identical, the 

 maximum increase of permeability will become less and less 

 as the force increases until for a certain force the curve begins 

 to cut the load-line. As the force increases beyond this value 

 the point of cutting approaches nearer and nearer to the origin 

 of coordinates, and the curve begins eventually to cut the 

 load-line in iwo points. The first point of cutting, as the 

 force increases still further, gets nearer and nearer to the 

 origin, whilst the second point gets further and further away 

 from it ; and when the magnetizing force reaches a value but 

 little over 3 C.G.S. units, the first point vanishes and the 

 second point only remains. Finally, w r ith a sufficiently high 

 force it would seem that the second point also cannot be 

 reached and the curve now lies entirely beneath the load-line, 

 whereas for very minute forces it lies entirely above this line. 



With nickel the curves for very minute magnetizing forces 

 are, like those of iron, exactly the same for different values of 

 the force, but instead of lying above the load-line lie entirely 

 below it. Beyond a certain limit of the force the curves 

 cease to be identical and the maximum decrease of per- 

 meability begins to become less and the curve near its origin to 

 bulge more and more towards the load-line, until for a value of 

 force a little over 21 C.G.S. units the permeability begins to in- 

 crease with small loads and to cut the load-line in one point, 

 which gets shifted further and further away from the origin 

 as the force increases. 



