334 Dr. J. R. Ashworth on Magnetic Hysteresis 



Again, with the four primary layers all in parallel and 

 Ri = 13*7 ohms (Ri/L^lSOO) the jar reduced the make-spark 

 from 9-0 to 3-9 mm. With ^ = 6*85 ohms (1^/1^ = 750)1116 

 jar diminished the spark from 13*2 to 6'6 mm. 



The secondary condenser doubtless acts also in another 

 way in modifying the secondary potential at make ; it alters 

 the effective resistance of the secondary circuit, which depends 

 to some extent on the frequency of the oscillation. In all 

 cases, however, it would appear that the condenser only affects 

 the make-potential by altering the effect of the damping 

 forces. The action of a secondary condenser in varying the 

 secondary potential at break is of an entirely different nature, 

 and arises from a different cause. This question will be 

 considered on a future occasion. 



Bangor, February 1917. 



XXXII. Magnetic Hysteresis treated according to Van der 

 Waals's Equation and the Kinetic Theory. By J. R. 

 Ashworth, D.Sc* 



Index to Paragraphs. 



T. 



1. Introduction. 2. Analogy between condensation of a vapour by 

 pressure and magnetization by the application of a field. 3. Van 

 der Waals's equation applied to fluid condensation and to ferro- 

 magnetism. 4. Critical constants. 5. The reduced equation. 

 6. The reduced hysteresis loop. 7. The field for instability and its 

 variation with temperature. 8. The anhysteretic isothermal, and 

 latent heat of magnetization. 9. The field-coefficient and corre- 

 sponding states. 10. Hysteresis in the relation I=/(T). 



II. 



1. Equations of the kinetic theory. 2. Graphic solution of the equa- 

 tions. 3. Tracing the hysteresis loop. 4. Determination of: 

 (a) Residual magnetism, (b) Intensity for instability, and (c) The 

 field for instability. 5. Variation of the field for instability with 

 temperature. 6. Corresponding states. 7. The question of critical 

 constants. 



III. 



1. Numerical values of the critical field deduced from the ferromagnetic 

 equation. 2. Vector character of intensity of magnetization and its 

 consequences. 3. Ratio of the intrinsic to the external field. 

 4. External critical field and field for instability. 5. Concluding 

 remarks. 



Communicated by the Author. 



