180 



Scientific Proceedings, Royal Dublin Society. 



In fig. 2 are plotted tlie values of the magnetic field or longitudinal 

 magnetisation as abscissae, and the total area of the cyclic curve or the circular 

 magnetisation as ordinates. The top curve is that obtained with the thickest 

 wire of cross-sectional area, O'l'T x 10"' sq. cms., and the lowest curve that got 

 with the wire of 6*5 x 10"' sq. cms. cross-sectional area. From tliese curves 

 we see that the circular magnetism rises to a maximum in a fairly weak 

 magnetic field, and tlien diminishes as the field strength is increased; and 

 also that the maximum circular magnetism in each of the several wires is 

 obtained for different values of the longitudinal magnetic field. 



Neglecting the lowest curve, since its peak or liighest point is somewhat 

 indefinite, if we pick off from the first four curves the value of the longi- 

 tudinal magnetic field corresponding to the highest point on each curve, and 



Magnetic field in c. g. s. units. 

 Fig. 2. 



plot these magnetic fields as ordinates against the corresponding values of 

 the cross-sectional area of the wires as abscissse, it will be found that the four 

 points lie practically in a straight line. 



This shows that when the cross-sectional area of the wire is increased 

 from 11'7 X 10"' sq. cms. to 54-7 x 10"' cms., or about 4"7 times, the longi- 

 tudinal magnetic field which [U'oduees tlie maximum circular magnetism 

 decreases from 3'3 to 1'5 c. g. s. units, or about 54 per cent. Again, if from 

 the same curves in fig. 2 we take tlie maximum circular magnetisation, or tlie 

 highest points attained in each of the first four curves, and plot the values as 



