A brown stone, in no respect presenting anything by which it shall be distinguished from other rude stones around it, is found, upon close examination, to possess the power of drawing light particles of iron towards it. If this stone is placed upon a table, and iron filings are thrown lightly around it, we discover that these filings arrange themselves in symmetric curves, proceeding from some one point of the mass to some other; and upon examining into this, we shall find that the iron which has once clung to the one point will be rejected by the other. If this stone is freely suspended, we shall learn also that it always comes to rest in a certain position,--this position being determined by these points, and some attractive force residing in the earth itself. These points we call its poles; and it is now established that this rude stone is but a small representative of our planet. Both are magnetic: both are so in virtue of the circulation of currents of electricity, or of lines of magnetic force, as seen in the curves formed by the iron dust, and the north pole of the one attracts the south pole of the other, and the contrary. By a confusion of terms we speak of the north pole of a compass-needle, meaning that point which is always opposite to the north pole of the earth: the truth being that the pole of the compass-needle, which is so forcibly drawn to the north, is a point in a contrary state, or, as we may express it, really a south pole. There is a power of a peculiar kind, differing from gravitation, or any other attracting or aggregating force with which we are acquainted, which exists permanently in the magnetic iron stones, and also in the earth. What is this power?