In the Weber-Ewing picture, each molecule of a magnetic substance behaves like a tiny magnet. Unmagnetised matter has random orientation, while magnetisation aligns many of these molecular magnets in one preferred direction.

• Random orientation gives zero net magnetic moment even though tiny dipoles exist inside the material.
• Magnetisation is described as realignment rather than creation of magnetism from nothing.
• Trap: do not conclude that an unmagnetised piece has no molecular magnets; it has no net moment because the orientations cancel.

A bar magnet is treated as two equal and opposite poles separated by effective length 2l. Effective length is smaller than geometric length, and for a standard bar magnet it is taken as five-sixths of the geometric length.

• Pole strength depends on material and cross-sectional area, not on the full length of the magnet.
• A freely suspended magnet aligns in the magnetic meridian, showing directive property.
• Trap: attraction is not the sure test of magnetism because iron is attracted too; repulsion is the decisive test.

Magnetic moment is M = m x 2l and is directed from south to north. When a rectangular magnet is cut into n equal parts in the manner shown in the text, the moment of each part becomes M/n, not M/root n.

• Mass becomes w/n and the dimensions of each part must be tracked explicitly before deriving new m and M.
• For a thin magnet, the scaling of length and moment of inertia changes further, so the thin-bar result should not be mixed with the rectangular-bar result.
• Trap: many students divide pole strength and effective length incorrectly and then lose the factor that gives M/n.