ON THE MAGNETIC QUALITIES OF IRON. 
1003 
These results are also exhibited, with others, in fig. 21. A reference to fig. 12 will 
show that the overlapping of one cyclic curve by the next lower curve (corresponding 
to a slightly narrower magnetic range) is characteristic of low cycles as well as of 
high ones. The loss of energy in reversal (measured by the area enclosed within 
the curve) becomes very small, both absolutely and relatively to the magnetization, in 
the lowest cycles; the molecular movements which constitute magnetization are there 
approaching the almost perfect reversibility which, as Lord Rayleigh has shown, is 
attained when the range of force is still further reduced. 
By way of further illustrating the behaviour of this sample under the weak 
magnetizing forces of the small cycles, fig. 13 has been drawn to show the total 
induced magnetism, and also the residual magnetism, in each small cycle, both in 
relation to H. The figure forms an interesting example of the early stages of the 
magnetizing process. 
The next sample (Ring V.) was also of thin sheet iron. It was sent by Mr. Parker, 
of the Electric Construction Corporation, as a sample of the iron used in building up 
the cores of his transformers. This iron is supplied in sheets about 6 feet long and 
3 feet wide, and its thickness is 0'367 millim. To make the ring, a strip 2 inches wide 
and 6 feet long was cut from the sheet, and this was coiled (along with a strip of paper 
for insulation) into a close spiral of the dimensions shown in the sketch (fig. 14), the 
-8-89- 
Section tLrousli Ring V. 
O O 
ends of the spiral overlapping one another for a centimetre or so. This is a convenient 
way of giving sheet metal the ring-form suitable for ballistic tests ; it is open, however, 
to the criticism that the bending of the metal is liable to harden it somewhat, 
especially near both surfaces, and it is possible that this consideration partly explains 
the comparatively sloping character of the curves (figs. 15 and 15a) obtained with this 
ring. A similar remark, of course, applies in the case of rings formed by winding soft 
iron wire. 
Cl :m 2 
