584 Intelligence and Miscellaneous Articles. 



assumption of absolute saturation is made. As this condition can 

 never be fulfilled in practice, the author redetermined the best 

 shape for the poles in an empirical way. It was found — in good 

 agreement with Prof. E wing's prediction — that it is best to take 

 a straight truncated cone of semi-vertical angle 60° (instead of the 

 theoretical 54° 44'). The field obtainable in air with such pole- 

 pieces falls short of the theoretical value by several thousand units ; 

 however, it beats the previous record (about 30,000 C.Gr.S.) by a 

 considerable amount. It was found — 



For a = 5 mm. ; H = 36,800 C. G. S. 

 „ a = 3 mm. ; H = 38,000 „ 

 where a denotes the diameter of the small truncated faces. 



To give an idea of this field the author points out that a bit of 

 good thin iron wire would easily get saturated up to 1 = 1750, 

 corresponding to an induction 



B = 38,000 + 4 ttX 1750 = 60,000 C.G-.S. 



This corresponds to a tension of B 2 /8?r dynes per cm. 2 , or 144 

 Kg-weight per cm. 2 A concentrated aqueous solution of ferric 

 chloride in a U-tube (Quincke) would be lifted about half a metre; 

 finally, the resistance of a bismuth spiral would be nearly trebled 

 in the field. 



The author concludes that it is possible to obtain fields of, say, 

 40,000 C.G-.S. with ring-electromagnets of reasonable size ; but 

 that stronger fields can probably only be reached by means out of 

 all proportion with the purpose in view. — Wiedemann's Annalen, 

 li. p. 537 (1894). 



ON THE THERMAL BEHAVIOUR OF LIQUIDS. 

 To the Editors of the Philosophical Magazine. 



GrENTLEMElSr, 



. The last number of your Journal contains a paper by Messrs. 

 Bamsay and Young, to which it would not be necessary to reply 

 if all your readers were familiar with the investigations on the 

 thermal behaviour of liquids. But as this cannot be assumed to 

 be the case, I am for the sake of my scientific reputation compelled 

 to reply. 



Messrs. Bamsay and Young reproach me with an error of obser- 

 vation of about 50° in the determinations of the critical point ; as 

 these authors well know, it would be impossible even for the most 

 inexperienced to make so serious a mistake. The liquid I used 

 had really the critical temperature stated, but I w r as in error in 

 relying upon the statement of the chemist who supplied me, that 

 the products were pure. 



The error is acknowledged by myself in the book I published, 

 and the critical temperatures I found are no longer given. But it 

 is too much to assume that a physicist who once in a way had the 

 misfortune to work with a mixture instead of a pure substance, 

 has become incapable of making a correct observation. 



Liege, May 7, 1894. P. de Heen. 



