442 Dr. Kaemtz on the Augmentation of 



periments themselves, I will develop a few formulae by which the 

 amount of the electro-magnetic power may be found from the 

 given angles of attradion or repulsion of the magnetic needle. 



M may therefore denote the power of the terrestrial mag- 

 netism ; 



VI the magnetic power of the needle, whose length is = 1. 



Now if the dipping needle is brought round an angle c out 

 of the magnetic meridian, then the terrestrial magnetism strives 

 to bring the needle into the meridian again, and with a power 

 too which is equal to 



M m. sin. c. 

 (Compare Hansteen on Terrestrial Magnetism, parti, p. 130. 

 Biot Precis de Phijsique, tom. ii. p. 26. edit. 2d.) 



The magnetic power of the connecting wire of the elec- 

 trical apparatus now acts on the needle likewise. If it be^ 

 required to calculate the amount of the magnetic power of 

 the electrical apparatus, from the angle of repulsion or at- 

 traction, where both powers (the terrestrial magnetism and the 

 electro-magnetism) are in equilibrium, there are two cases to 

 be distinguished : namely, the connecting wire either passes 

 through the magnetic meridian, or forms an angle with it. 



a) If the electrical stream 

 passes through the magnetic meri- 

 dian below the needle from south 

 to north, and above it from north 

 to south; thus does it pass in SN ; 

 then it has on the western side a 

 southerly, and on the eastern 

 side a northerly polarity. The -5^ 

 north pole of the needle [pole 

 austral of the French) is driven 

 towards the east, and the needle 

 remains stationary in ns. 



Now E may denote the mag- 

 netic power of the connecting 

 wire : this acts in a direction 

 perpendicular to the axis of the wire, towards DE. Therefore 

 we may at the same time take for granted, that DE is pro- 

 portional to the magnetic power. We therefore change DE 

 into DG and GE, hi which case DG is perpendicular to ns. 

 Now the relation is. 



DE : DG = 1 ; cos EDG, that is, 

 E : DG= 1 : cos c is consequently 

 DG = E cos c. 

 Ilie needle reacts against this power with the power m ; the 



electro- 



