86. The Dip or Inclination of the Magnetic Needle. The needle is said to dip when it takes positions like those in [Fig. 24]. Compass-needles should be horizontal, when properly balanced, and entirely free from all effects other than those of the earth. The excessive dip shown ([Fig. 24]) is due, of course, to the efforts of the magnetic needle to place itself in the direction in which the lines of force of B M pass.
EXPERIMENT 46. To study the dip or inclination of the magnetic needle, due to the action of the earth.
Apparatus. [Fig. 25]. Our compass, O C (No. 18); horseshoe magnet, H M (No. 16); piece of paper.
87. Directions. (A) Place O C upon the table, and mark upon a piece of paper the height of the N pole of its needle above the table. ([Fig. 25].) The paper should be held in a vertical position, and near the pole.
(B) With H M reverse the poles of the compass-needle ([Exp. 13]), so that its former N pole shall become a S pole.
(C) Place the needle upon its pivot again, and mark upon the paper, as before, the height of its new N pole above the table. Does the needle remain horizontal?