327 



Table III (p. 326) shows the values of the wind velocity, the 

 direction of the wind and tlie angle of deviation as calculated from 

 equation (2) for 16 different directions of the gradient and a uniform 

 field of 1 mm. difference of pressure per degree of latitude. 



A comparison of these results with those of table II .shows that 

 the use of an average wind for the whole country has induced a 

 more regular course in the numbers, but also that considerable 

 differences are due to this method. The wind \elocity and the angles 

 of deviation have become smaller as also the azimuths and wind 

 directions. From this result we may conclude that the northerly 

 stations behave differently in many respects from Flushing and that 

 a combination as made in (his in(piiry is not dcsiiable. 



Physics. — "On a (jeiu-rnl Electromagnetic Thesis and its Application 

 to the Maf/iietic State of a. Ttristed Iron Bar". By Dr. It. J. 

 Elus. (Communicated by Prof. H. A. IjOrrntz). 



(Gommunicatod in the meeting of May 29, 1915). 



WiKDEM.'VNN has already observed that in a longitudinally resp. 

 circularly magnetized iron bar a circular resp. longitudinal magneti- 

 sation arises in consequence of torsion. Moreover he discovered that 

 a bar which is at the same time longitudinally and circularly 

 magnetized, is twisted. These observations formed the starting point 

 of the following considerations. 



In a magnetic field, in which the magnetic induction can be an 

 arbitrary vector function of the magnetic force variable from point 

 to point, whereas (he media in the field can be anisotropic also \vith 

 respect to the conductivity, but in which no phenomena of hysteresis 

 occur, the equation 



T = - C^L U/M') 



(I) 



holds for the liiagnetic field energy. 



In this / means the current in a circuit M, the induction fluX 

 passing through this circuit, c representing the ratio of the electro- 

 magnetic to the electrosfalic unity of electricity. The summation 

 extends over all (he circuits, the integration covering a range from 

 M for / = to the final value which J/ assumes. 



') in lliiis and folldwing t'orinulae LorenTz's system of unities is iise<l. 



22* 



