A new formula for the penetration time of large Barkhausen discontinuities is given which is based on definite assumptions regarding the condition for magnetic reversal. In order to bring this formula into agreement with experimental results, it must be modified by the introduction of a length of 0.035 cm of unknown origin. The modified formula agrees well with the results observed for wires of various diameters, a strip, for various impressed fields, tensions and torsions, and for variations of jump magnitude and electrical resistivity. The behavior of the discontinuity in a 15 percent NiFe wire relative to heat treatment was investigated. Changes in critical (minimum propagating) and coercive fields were indicative of the internal state of strain in the wire. The presence of cold-work strains appears to be necessary for the occurrence of the jump but the addition of strains arising from cooling through the $\gamma -\alpha$ transformation reduces the tendency to form the large discontinuity. Propagation was observed at temperatures up to 350°C. With increasing temperature the slope $A$ of the $v-H$ curves increased. At the same time the range between the critical field and the field at which propagation starts spontaneously at some point in the wire decreased. Etching the surface of a wire also increased $A$ and decreased propagation range. Cracks appearing in the wire surface indicated that the release of surface strains may well have been responsible. It was established that neither the removal of material nor the absorption of hydrogen were the cause.

• Received 9 September 1932

DOI:https://doi.org/10.1103/PhysRev.42.419