The Gouy's method involves measuring the force on the sample by a magnetic field and is dependent on the tendency of a sample to concentrate a magnetic field within itself.
The solid sample in the form of a long cylinder (area of cross section A) is hung from the pan of a balance and is placed such that one end of the sample is between the pole-pieces of the magnet (field H) and the other one is outside the field.
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The force exerted on the sample by the inhomogeneous magnetic field is obtained by measuring the apparent change ( m ) in the mass of the sample. The susceptibility χ is given By 2χ = 2 Δ mg/AH If the sample is in the form of powder, it is filled in a long nonmagnetic tube which is then suspended from the pan of the balance.