Uè 



phases of a heart period that has bee» registered by derixation 1. 

 for instance, and of another period by derivation II or III. 



Moreover, one heart contraction is not exactly lil<e another. At a 

 superficial glance the E.K.G. of the same series, appear so similar 

 to one another, that one would take one period for the reproduction 

 ot another, but, when measured, numerous small differences appear 

 whicli impede the accurate calculation of the direction and the 

 manifest value of the potential difference. All these difficulties disappear 

 when the E.K.G. is registered bj' the three derivations simultaneously. 



The method is of service not only physiologically, but also clinically. 

 For the object of practical cardiography is not to ascertain the 

 [)0tential difference that exists between one hand and another, or a 

 hand and a foot, but to obtain an insight into the working of the 

 heart itself). 



Physics. — "ÏVic indgnetic suscepti/>i/ifi/ antl the nuinher of HKtif- 

 netons of nickel in solutions of nickelsaJts." By P. Weiss 

 and Miss E. D. Bruins. (Communicated by Prof. H. A. 



LÖRENTZ.) 



§ 1. The purpose of this research was to investigate, how in 

 connection with the magnetontheory the magnetic susceptibility of 

 nickel in solutions of nickelsalts depends on the concent lation of 

 nickel in the solution. The i-esearch was made after Quincke's method 

 improved by Picc.\rd'j. 



Before and after every series of measurements water was measured 

 of which the specific susceptibility or coefficient of magnetisation 

 has of late years been determined with great accuracy after different 

 methods. 



For this coefficient Séve gives : — 0.725.10-6 at 22° C. ') 

 Picc.ARD : — 0.7193.10-'> „ 20° C. ') 

 DE Haas and Drapier : —0.721.10-6 __ 21° C. 

 In the following calculations has been used the value given by 



PiCCARD -/iu-aler 20» C. = 0.7193.10—6. 



The coefficient of magnetisation X/^ of the solution is calculated 

 with the formula: 



1) Tlie complete account of liie above investigation wifl appear elsewliere. 

 -; Die Magnetisieiungskoeffizienten des Wassers und des Sauerstoiïs. Promotions- 

 arbeit von A. Piccahd. Arch, de Geneve 1913. 

 ') SÈVE. Paris ]9f2. Tlièse. Ann. Cliim. pliys. (8) 27 p. 189-244. 1912. 

 ^) Dr Haas und Drapier. Annalen der Physik. Band 42. p. 673-684. 1C13. 



