﻿766 Dr. A. Sellerio on the Repulsive Effect upon 



It may be well to give an outline of my apparatus : a sort 

 of torsion balance, shown in plan in fig. 1 (from the JSuovo 

 ■Cim.). 



At were connected to the horizontal rod a suspension 

 fibre normal to the plan hanging down from a graduated 



Scfi 



ermo 



torsion head, and a little iron style dipping into a mercury 

 trough. Therefore the current flowed through the mercury 

 either in the direction OMB A, or in the opposite one. 

 Further details are referred to loc. cit. 



When the arc is started, the arm OM tends to recoil, and 

 to hold it stationary it is necessary to give to the fibre a 

 certain torsion a, corresponding to a force 



F = 0*036 a dyne. 



In the force F there are to be distinguished : — 



The true repulsion rising within the arc gap ; 



Some disturbance occasioned from the heat, as air 



convection currents, etc. ; 

 The influence Y of the earth's magnetic field ; 

 The electro-dynamic action E between OMB and the 

 - fixed circuit. 



2. The earth's action V can be easily calculated, as 

 follows : — 



As the arm OMB is free to turn about a vertical axis, the 

 recorded forces are only the horizontal one, and consequently 

 the earth's field is acting upon OMB only with its horizontal 



