Contributions to terrestrial magnetism
In the present number of these contributions, the author resumes the consideration of Captain Sir Edward Belcher’s magnetic observations, of which the first portion, namely, that of the stations on the north-west coast of America and its adjacent islands, vas discussed in No. 2. The return to England of H. M. S. Sulphur by the route of the Pacific Ocean, and her detention for some months m the China Seas, have enabled Sir Edward Belcher to add magnetic determinations at thirty-two stations to those at the twenty-nine stations previously recorded. The author first describes the experiments which he instituted with the different needles employed by Captain Sir Edward Belcher for determining the coefficient to be employed in the formula for the temperature corrections; and takes this opportunity of noticing the singular fact that, in needles made of a particular species of Russian steel, this coefficient is negative; that is, in these needles, an increase of temperature increases the magnetic power. M. Adolphe Erman describes this particular kind of steel as consisting of alternate very thin layers of soft iron and of steel, so that when heated the soft iron layers increase their magnetic intensity and the steel layers diminish theirs.