Intelligence and Miscellaneous Articles. 393 



relative width of the ring d/r. The empirical expression for tbis 

 dependence is a linear one of the form 



r 



where h is a constant which, for the Swedish iron investigated, has 

 the value 7, and will presumably have values differing but little 

 from this in the case of other ferromagnetic metals. This will 

 probably be the case more especially in the kinds of iron used in 

 technical processes. 



5. "When the empirical constant h is known, the factor of 

 demagnetization can be calculated from the geometrical dimensions 

 of the system bv the formula 



% m 



K)( i+ *9 



d \ ' v 



in which p is the radius of the ring, r that of the section, and d 

 the width of the slit. This formula holds with the same limitation 

 as (1), (2), and (4), that is, up to demisaturation. In general the 

 equation holds, 



('-^ 



in which v is the factor of dispersion. 



6. For high magnetizing values the factor of demagnetization 

 approaches the limiting value 



a 



The previous results may find an approximate application even in 

 imperfect magnetic circuits of complicated shapes. — Wiedemann's 

 Annalen, No. 3, 1893. 



THE SPECIFIC HEAT OF LIQUID AMMONIA. 

 BY C. LUDEKING AND J. E. STARK. 



The specific heat of liquid ammonia, though it has of ten been the 

 subject of calculation in development of theory and practice, has 

 not yet been satisfactorily determined experimentally, if we except 

 the work of Eegnault. His results, however, were unfortunately 

 lost during the Paris Commuue. He assumed the specific heat to 

 be 0*799. Since then the interest in this constant has very 

 considerably increased through the rapid development of the 

 artificial ice industry. Generally the specific heat has been taken 

 at unity. Thus De Volson Wood in his ' Thermodynamics,' 

 page 337, recommends this value " until the experimental value is 

 determined." 



It was our good fortune to have ready access to all the means 

 necessary for executing the somewhat laborious experiments 

 involved, and we take this opportunity to present briefly the 



