26 
Proceedings of the Royal Society of Edinburgh. [Sess. 
similar in their main features, in which the induction changes are plotted 
against decreasing values of field as abscissae for various intensities 
represented as the case may be by the number of 1 mm. sparks in series for 
co-directional oscillations, the length of the single spark for transverse 
oscillations, and the function W x D° 7 for mechanical vibrations. 
It may be noted, however, that the range of decreasing cyclic field over 
which the neutral points may shift with variation in the intensity of the 
oscillations (fig. VIII. co-directional oscillations, fig. X. transverse oscillations) 
is much greater than that obtained with mechanical vibrations, fig. II. 
Cyclic Residual Magnetisation . — Garibaldi obtained increase, Maurain 
a very small decrease,* of cyclic residual magnetisation upon the super- 
position of electric oscillations. These isolated results are in harmony with 
those obtained with mechanical vibrations. Any elaborate experiments were 
therefore considered superfluous with electric oscillations. 
III. Results with Cyclic Field and Cyclic Residual Magnetisation 
in Terms of Field Change. 
The experimental results for cyclic field and cyclic residual magnetisation 
now fall to be compared, the one with the other. The comparison will be 
facilitated if the starting-point be made from one or other of the cyclic 
extremes in both cases, say from the positive extreme, as represented in all 
the diagrams. In the former case, when vibrations or oscillations are 
superposed at all points of the descending arm of the normal hysteresis 
loop, the induction change at the cyclic extreme is positive, as the cyclic 
extreme is just departed from also positive, afterwards negative or positive 
as the intensity of the vibrations or oscillations is weak or strong, beyond 
the lower limiting value of the neutral points and until zero field is reached 
negative, between zero field and the negative cyclic extreme also negative. 
In the latter case, where vibrations or oscillations are superposed at all, 
values of cyclic residual magnetisation reached by the cyclic field process 
from the positive amplitude, the induction change at the residual extreme 
is negative, as this position is just departed from also negative, afterwards 
positive or negative as the intensity of the vibrations or oscillations i& 
weak or strong ; beyond the lower limiting value of the neutral points (for 
the strongest intensity used) and until zero magnetisation is reached 
positive, and finally between zero magnetisation and the negative extreme 
of cyclic residual magnetisation also positive. 
With cyclic field and cyclic residual magnetisation alike, the shift of the 
* u presque nulle ” ; see p. 2. 
