38 Proceedings of Royal Society of Edinburgh. [sess. 
Second. The iron is again demagnetised and subjected to 
co-direction al oscillations, upon which the field at the same fixed 
maximum value is superposed. After twenty reversals of field, 
the hysteresis loop is determined as before. 
Third. The iron being again demagnetised, the same process is 
repeated for transverse oscillations and the corresponding measure- 
ments made. It is, of course, understood that in cases second and 
third the force sustaining the oscillations remains “ on ” and 
unaltered until the series of galvanometer readings has been 
completed. 
The above determinations were repeated for many field cycles, 
the maximum induction values at the extremes of each cycle 
ranging from a minimum of B = 20 to B= 12,000. 
Summary of Results under B conditions. 
Permeability * — See fig. 3, where the full line, dotted line, and 
dash line curves have the same signification as in figs. 1 and 2. 
For low values of field co-directional oscillations increase the 
permeability relative to the normal (i.e. without oscillations) to a 
greater extent than transverse oscillations. 
For higher values of field transverse oscillations, increase the 
permeability relative to the normal to a greater extent than co- 
directional oscillations. 
The crossing point of these curves occurs when the induction 
is about 5000 with oscillations. 
When the induction does not exceed a few hundreds without 
oscillations, the corresponding induction with transverse and 
co-directional oscillations is respectively about three and four times 
greater. When B = 20 without oscillations, these ratios become a 
little less. 
Retentivity . — When the field is reduced to zero from a cyclic 
maximum and the ratio of residual to maximum induction plotted, 
as in fig. 5, against maximum cyclic induction, the curve with 
transverse oscillations is higher within wide limits than that 
obtained with co-directional oscillations. These curves appear to 
coalesce, or even to cross, in higher fields. The normal retentivity 
curve lies above both. 
* After twenty reversals of field. 
