among miners, signifies the interruption or breaking off the veins of ore; an accident which gives them a great deal of trouble before they can discover the ore again. See Mining.

Dipping Needle, an instrument used for observing the quantity of inclination towards the earth, assumed by any needle or other body after it has acquired the magnetic virtue. This was first observed by one Robert Norman, an Englishman, and a maker of compasses for mariners, in the end of the sixteenth century, who finding that he was always obliged to counterbalance that end which turns to the north by a bit of wax or such other substance, though the balance had been ever so exact before, published an account of his discovery as a matter of importance. The subject was instantly attended to; and instruments were not only contrived for ascertaining the quantity of the dip, but various speculations were formed concerning the cause of so surprising a phenomenon.

The general phenomena of the dipping needle are, that about the equatorial parts of the earth it remains in a horizontal position, but depresses one end as we recede from these; the north end if we go towards the north, and the south end if we proceed towards the south pole. The farther north or south that we go the inclination becomes the greater; but there is no part of the globe hitherto discovered where it points directly downwards, though it is supposed that it would do so in some part very near the pole. Its inclination is likewise found to vary very considerably at different times in different places of the earth, and by some changes of situation, in such a manner as must appear at first sight very unaccountable. Of all those who have attempted the investigation of this obscure subject, none has been more successful than M. Cavallo, who in his Treatise on Magnetism has paid particular attention to all the phenomena, and accounted for them upon plain and rational principles. The voyages to the arctic regions, in search of a north-west passage, have led to a great accumulation of observations by means of the dipping-needle. See Magnetism.