Laboratory experiments on the magnetization of rocks

Specimens of natural rock masses collected by H.M. Geological Survey were tested for magnetic susceptibility and permanent magnetization before and after various artificial treatments. After cooling in the earth's field, cut cubes were found to be magnetized with an intensity much greater than that of the natural rock, and the values decayed very little with time. When artificially magnetized in the cold, the cubes were only affected by fields above a certain value, and the decay was often considerable. Curves are given showing the decay with time and the demagnetization of the heated cubes by increasing fields. The susceptibility of natural rocks increases with the field, in some cases reaching a maximum between 50 and 100 C.G.S. These results are compared with data by J. G. Koenigsberger.