The work reported on here is an investigation of the radial distribution of electrical conductivity σ in the earth's mantle. Previously this function had been inferred only to about the 800‐km depth from the geomagnetic transient variations of external origin (see Lahiri and Price). Throughout the remaining lower portion of the mantle, we make use here of the longer wave periods which characterize the geomagnetic secular variation. Choosing a power law for σ, the wave attenuation and phase retardation after propagation through the mantle are investigated, using sinusoidal input functions, and an equivalent conductivity is established on the basis of amplitude attenuation. Aperiodic models at the core are solved by the method of Laplace transforms and a time discontinuity inHr. (δ‐function inHr) is treated in detail. The elapsed time for a pulse to reach the earth's surface is expressed in terms of an equivalent conductivity. The latter quantity is then gotten indirectly from a study of the time‐dependent magnetic observatory records. Judged somewhat better than an order of magnitude, in these calculations, σ is shown plotted throughout t