To communicate the magnetic power to a needle, let it be placed horizontally, and with a magnet in each hand, let the north pole of one, and the south pole of the other be brought, obliquely, in contact over the centre of the needle ; draw them asunder, taking care to press firmly, and preserving the same angle or inclination to the very ends of the needles, which should be supported by two magnets, whose ends ought to correspond in pola rity with those of the needle. Observe to carry the magnets you press with clear away from the ends of the needle, at least a foot therefrom ; repeat the friction in the same manner several times, perhaps six, eight, or ten times, and the needle will be permanently magnetized. As we have already stated, by using other magnets in succession, the powers of the needle will be proportionably increased. But no el feet will result from the friction if the bars are rusty, or, indeed, not highly polished ; their angles must be perfect, and their several sides and ends com pletely flat.
It is, perhaps, one of the most curious of the phenomena attendant upon this occult property, that the centre of every magnet is devoid of attraction ; yet, that when a needle is placed in a line with a magnet, and within the influence of its pole, that needle also becomes magnetic ; or, rather, a conductor, possessing a cer tain portion of attractive power : and it is no less extraordinary, that the magnet retains its power even in the exhausted receiver of an air.pump: this seems to be a formidable objection to its being influ enced by any fluid. Perhaps the opinion entertained by many of our most popular lecturers on this subject, viz. that the earth itself is the great attractor, may be nearest the truth. We are the more sup posed to incline towards such an hypo thesis, knowing that, at the true magne tic equator, the needle does not dip ; and from the well ascertained fact, that bars of iron, placed for a length of time exactly perpendicular, receive a strong magnetic power, their lower ends repelling the south, but attracting the north poles of magnets applied to them respectively.
The direction of the dipping needle was ascertained by one Hobert Norman, about two hundred and fifty years ago. Ile suspended a small magnetic needle, by means of a fine thread around its centre, so as to balance perfectly, over a large magnet : the south pole of the former was instantly attracted by the north pole of the latter. He found that so long as the needle was held exactly centrical, at about two inches above the magnet, it re mained horizontal : but so soon as with drawn a little more towards one end than the other of the magnet, the equilibrium was destroyed, and that pole of the nee dle which was nearest to either pole of the magnet was instantly attracted, and pointed downwards thereto. By the mag netic equator, we mean a circle passing round the earth at right angles with the magnetic poles, which do not correspond with the geographical poles, as may be fully understood by the indications of all compasses to points differing from the latter and as the indications of com passes vary so much, both at different times and places, we may reasonably conclude, that the magnetic poles are not fixed. The variation of the dipping needle has not, in our latitude at least, varied more than half a degree since its depressive tendency was first disco vered by Norman.
The suspension of Mahomet's body, in the temple where it was deposited, is supposed to have resulted entirely from magnetism, with which the Arabians were completely unacquainted.