188 



Scientific Proceedings^ Royal Dublin Society. 



ordiuates against the corresponding values of the cross-sectional area of the 

 wires as abscissae, it will be found that these four points lie practically in a 

 straight line. It will be seen from this that when tlie cross-sectional area 

 of the wire is increased about 4'7 times, the longitudinal magnetic field which 

 produces the maximum circular magnetisation decreases from 3'5 to 2'5 e.g.s. 

 units, or about 28 per cent. If from the same curves in fig. 6 we take the 

 maximum circular magnetisation in each of the four curves, and plot these 

 values as ordinates against the corresponding values of the cross-sectional 

 areas of the wires as abscissse, the points will also be found to lie very 



Magnetic field in c. g. s. units. 

 Fig. 6. 



approximately in a straight line, showing that when the cross-sectional area 

 of the wire is increased about 4'7 times, the maximum circular magnetism is 

 increased about three times. 



The following conclusions may be arrived at from these experiments : — 

 A. When a mechanical twist is given to the wire and the transitory 

 electric current measured : — 



1. In an iron wire under constant longitudinal stress and magnetised 

 longitudinally, tlie circular magnetisation rises to a maximum 

 in a weak magnetic field ; and the value of the longitudinal 



