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III, The Magnetic Temperature Coefficients of the Ferro- 

 magnetic Elements in Corresponding States. By J. ii. 

 ASHWORTH, D.Sc* 



1. Introduction, and initial statement of the final result. 



2. Description of experimental work. 



3. Results of experiments in tables and ding-rams. 



4. Comparison of results with similar experiments by other 



observers. 



5. Reduction of results to corresponding states and conclusion 



therefrom. 



6. Comparison with the temperature coefficient of density of a 



liquid. 



7. Curie's law for paramagnetics. 



8. Analogy between fluids and ferromagnetics. 



1. A FTER a magnet has been repeatedly heated and 



Jr\. cooled over a given range of temperature the mag- 

 netic intensity falls and rises regularly and in general without 

 hysteresis as the temperature is raised and lowered. It has 

 been shown that the magnitude of this effect of change of 

 temperature on the magnetic intensity is largely controlled 

 by the dimension ratio of the magnet, and that when this 

 ratio is very large, so that the demagnetizing factor is negli- 

 gible, the temperature coefficient is then a minimum, and 

 under these conditions is characteristic of the material of the 

 magnet t- 



In the course of experiments on this subject, it was ob- 

 served that the temperature coefficient of nickel was large, 

 that of iron small, and that of cobalt still less, the values 

 then obtained over a range of temperature of 90°, from 10° 

 to 100° 0., being about 6 X 10 -4 for nickel, 2 x 10~ 4 for iron, 

 and 1*5 x 10 ~ 4 for cobalt. 



A preliminary calculation indicated that the characteristic 

 coefficients were a function of the critical temperatures of 

 these ferromagnetics, a result which demanded a more com- 

 plete investigation. This has now been made, and the 

 present paper is a record of experiments upon the variation 

 of residual magnetic intensity of magnets made of nickel, 

 iron, and cobalt of large dimension ratio, containing as little 

 impurity as possible, when the temperature fluctuates between 

 that of the atmosphere and the critical temperature. 



The evidence now obtained supports the tentative con- 

 clusion mentioned above, and allows the general statement 

 to be made that the characteristic temperature coefficients of 



* Communicated bv the Author. 



t Ash worth, .Roy. Soc. Proc. vol, lxii. p. 221 (1897) : Phil. Trans. Roy 

 Soc. vol. ciii.. 1903. 



