Checking of square-law detectors used in Hartshorn and Ward dielectric measurements

It is shown that the ratio of resonance widths test, which is intended to check the square law of detectors used in Hartshorn and Ward measurements, does not give positive proof of compliance to a square-law characteristic. It is further shown that this test is insensitive to a likely form of departure from square law, which will give rise to errors in both conductance and loss-tangent measurements. An example is provided and general conclusions are drawn relating to the experimental verification of the compliance of detectors to a theoretical law.