It is not possible, or at least it has hitherto not
been found possible, to embody all these various elements into an exact
mathematical formula, which would give the magnetic moment as a function
of the exciting current; but the above mentioned experiments have shown
that within certain limits, and in the neighborhood of the point of
saturation, the relation between the two is that of an arc to its
geometrical tangent. It will be seen that for large angles the arc
increases much slower than the tangent; that is, for strongly excited
cores, a very large increase of the exciting current will produce only
a slight increase of magnetic moment. If Mueller's formula were correct
for all currents, absolute saturation could only be reached with an
infinite current. Whether this be the case or not, it is certain that
the greater the exciting current the less will a variation in it affect
the magnetic moment of the core. To imitate as nearly as possible
permanent steel magnets, it is therefore necessary to use electro
magnets, the cores of which are easily saturated.
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