308 Intelligence and Miscellaneous Articles. 



In addition, M. Boltzinann remarks that the magnetizing of a 

 ring can be most easily calculated by introducing Carl Neumann's 

 coordinates, and that the absolute value of the velocity of the elec- 

 tricity in a current can be calculated from E. H. Hall's recently 

 published uncommonly interesting experiments. If the gold leaf 

 employed by Hall, of the length I and breadth 6, is in a homoge- 

 neous magnetic field of the intensity m (measured in absolute Gauss 

 measure), the electromagnetic force which tends to impel it perpen- 

 dicular to the lines of magnetic force has the intensity 



in which J m is the intensity of the current passing through the gold 



leaf in the direction of its length (in magnetic measure), J e is the 



same current-intensity measured in Weber's electrostatic or mecha- 



metres 



nical measure, v is equal to 31-10 7 f . If in the time t the 



* second 



quantity of electricity e passes through the cross section of the 



n s>c W16G 



gold leaf with the velocity*?, then is J e = - = y, and hence 7c= * 



If now at two places in a conductor, separated by the distance 6, 

 the difference of potential p prevails, in its interior the force •; 

 acts upon the unit amount of electricity, upon the amount e the 

 force -J-. Hence, if the force above denoted by 1c itself acts upon 



the movable electricities in the gold leaf, and the potential-differ- 

 ence thereby produced between the two extremities of the gold leaf 



ii „ . 7 pe kb mbc __ 



be denoted byp, then is fc= y, p= — = — -. JNow let the two 



extremities of the gold leaf be connected with a galvanometer. The 

 total resistance of this circuit (gold leaf, galvanometer, and con- 

 ducting-wires) shall be denoted by w 9 and i shall denote the cur- 

 rent-intensity produced therein by the magnet, while again the 

 index m signifies magnetic, the index e mechanical measure of the 



current. Then is i p — ~ = , i m = , from which it follows 



iv. vw'J w m 



1 in e e m 



Ln<tt o — — . ]? rom this formula the absolute velocity c of the 



electricity in the current J can be determined. It is exactly equal 

 to the velocity with which a wire of length b must be moved, per- 

 pendicular to itself, through the magnetic field, in order that it may 

 generate the current i in a circuit of resistance w. In this the wire 

 is supposed to be parallel to the length, the direction of its motion 

 parallel to the width, of the gold leaf. If we put i m iv m =:e m , then e m 

 is the electromotive force, in magnetic measure, which would pro- 

 duce in the same circuit the same current i m . Its measurement 

 suffices for the calculation of c. In order to obtain the general 

 theory of Hall's phenomenon, the equations constructed by Kirch- 



