The Gouy balance, invented by Louis Georges Gouy, is a device for measuring the magnetic susceptibility.
In use, a long, cylindrical sample to be tested is suspended from a balance, partially entering between the poles of a magnet. The balance measures the apparent change in the mass of the sample as it is repelled or attracted by the region of high magnetic field between the poles. Some commercially available balances have a port at their base for this application.
In a practical device the whole assembly of balance and magnet is enclosed in a glass box to ensure that the weight measurement is not affected by air currents. The sample can also be enclosed in a thermostat in order to make measurements at different temperatures.
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