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The Magnetic Condition of the Earth

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-308

2025-11-29

627

We have seen that the + pole of a magnet repels the + pole of a needle and attracts the - pole. We have also seen that the needle tends to set itself in the direction of the lines of force, and that a magnetic needle, suspended so as to swing freely, points with its north end toward the magnetic north. It is evident, then, that the earth acts as a great magnet, and that the pole toward which the north-seeking end of the needle points has the same kind of polarity as the -or south end of a bar magnet. The fact that the north magnetic pole of the earth and Figure 1 shows a form of needle that is used to determine the dip. It consists of a magnetic needle swinging on a horizontal axis which is in a direction perpendicular to the magnetic meridian. The needle itself swings in a vertical plane in the magnetic meridian. It is so balanced that it will come to rest in a horizontal position before being FINDER magnetized. After it is magnetized and placed in the magnetic meridian it will set itself in the line of dip.

The miner's dipping needle, Fig. 2, is a portable instrument of the same general type, that is used to detect the presence of magnetic ores. 

FIG.1

the north pole of a magnetic needle are of unlike signs has given rise to some difficulty in giving them names that are scientifically correct; but the name north for the + pole of the needle is generally adopted.