| This dip needle in the Collection of Historical Scientific
Instruments at Harvard University, was made by Thomas Hall of Boston. Hall
took over Daniel Davis' business in the 1850s and the company later became
Palmer and Hall.
The 1841 edition of the Manual of Magnetism says that "If the needle be suspended so as to have freedom of motion in a vertical direction, it is found not to maintain a horizontal position, but one of its poles (in this hemisphere the north) inclines downward toward the earth. At the magnetic poles of the earth the direction of the needle would be vertical; but the inclination diminishes as we recede from the poles toward the equator, and at the magnetic equator, which is near the the geographical one, the needle becomes horizontal. A needle properly prepared for exhibiting this inclination, is called a dipping needle."