"The increase in the accuracy and completeness of magnetic observations which was obtained by the new method opened up fields of research. [There are] disturbances to which the magnetism of our planet is found to be subject. Some of these disturbances are periodic following the regular courses of the sun and moon. Others are sudden, and are called magnetic storms, but, like the storms of the atmosphere, they have their known seasons of frequency. The last and the most mysterious of these magnetic changes is that secular variation by which the whole character of the earth, as a great magnet, is being slowly modified, while the magnetic poles creep on from century to century along their winding track in the polar regions. We have thus learned that the interior of the earth is subject to the influences of the heavenly bodies..."