In this fact we have a symbol which tells us that the earth represents a polarity of the second order, with its 'salt'-pole in the north and its 'sulphur'-pole in the south. Hence the magnetism called 'North' must be of saline and therefore spherical nature, corresponding to the negative pole in the realm of electricity, while 'South' magnetism must be of sulphurous - i.e. radial-nature, corresponding to positive electricity. Moreover, this must hold good equally for the fields of magnetic force generated by naturally magnetic or artificially magnetized pieces of iron. For the circumstance that makes a piece of matter into a magnet is simply that part of the general magnetic field of the earth has been drawn into it. Of especial interest in this respect is the well-known dependence of the direction of an electrically produced magnetic field on the position of the poles of the electric field.