Abstract: Method and apparatus for determining the nature or property of a non-metallic material in which the material is passed through a time varying magnetic field. The signals which are induced in the sensing coil for the magnetic field are processed for measurement. Although the material is non-metallic, it may have sufficient conductivity at the frequencies employed to cause the flow of eddy-currents to generate a measurable signal. The method of the invention also provides for measurement of permittivity or diamagnetic properties of the material which may also give rise to small measurable signals.