Page:Electricity (1912) Kapp.djvu/151

force will be experienced at any point of the sphere, and the only thing that changes will be the direction of the line along which the force acts. We may in fact, analogous with the argument used in the consideration of the electrical problem, consider the magnetic force as an attribute of space and express it by the product B × m, where B indicates the density of the magnetic field on the surface of the sphere of radius D. B is the "induction" expressed as so many lines of force per square centimetre of surface, and the product of the total surface of the sphere, with this induction, will give the total flux of force $\Phi$ emanating from the magnetic mass M. Since the surface of a sphere is $4\pi \mathrm {D} ^{2}$ and $B={\frac {M}{D^{2}}}$, we find the following relation between the quantity of magnetic matter M and the total flux $\Phi$ emanating from it—

$\Phi =4\pi \mathrm {M}$

We are now in a position to define unit of induction and unit of magnetic matter. If two magnetic masses placed one centimetre apart attract or repel each other with the force of one dyne, then each magnetic mass has unit value. If at any point of space unit