Production of the field of a defect by magnetization by the moving field of a localized source

Results are given on the origin and structure of the field due to a transverse crack when the specimen is magnetized by the longitudinal moving field of a localized source. The causes of the field are deduced from oscillograms of the magnetization of parts near the faces of a natural crack in a rail at speeds up to 25 km/hr. The results may be used to evaluate proposed modifications to the probes of high-speed flaw detectors.