The requirements of barley within the soil, and its susceptibility to the external influences of season, are very similar to those of its near ally, wheat.
The magnetic susceptibility expresses the numerical relation of the magnetization to the magnetizing force.
Those substances which are attracted, or rather which tend, like iron, to move from weaker to stronger parts of the magnetic field, are termed paramagnetic; those which are repelled, or tend to move from stronger to weaker parts of the field, are termed diamagnetic. Between the ferromagnetics and the paramagnetics there is an enormous gap. The maximum magnetic susceptibility of iron is half a million times greater than that of liquid oxygen, one of the strongest paramagnetic substances known.
Bismuth, the strongest of the diamagnetics, has a negative susceptibility which is numerically 20 times less than that of liquid oxygen.
From the equation K=(µ - I)/47r, it follows that the magnetic susceptibility of a vacuum (where µ = I) is o, that of a diamagnetic substance (where, u < I) has a negative value, while the susceptibility of paramagnetic and ferromagnetic substances (for which µ> I) is positive.