E. W. Davis

“ It is well to remark that the curves representing magnetic variations and auroras lag about six months behind those representing the sun-spot variations. The sun-spot area seems in some way to depend upon the position of the planets. Not only is the earth's magnetism thus, seemingly at least, influenced by the sun-spots, but also some of the phenomena of the weather. ”

“ The pulley is turned into such a position that the pull of the suspension skein brings the magnet approximately at right angles to the magnetic meridian. The magnet is in equilibrium under the action of three forces: gravity, the pull of the threads, and the horizontal component of the earth's magnetism. The first two forces being constant, the equilibrium is not destroyed save by a variation in the intensity of the third force. The changes in the direction of that force are never sufficiently great to appreciably alter the position of this magnet. ”

“ Thus, if the north-seeking pole of the magnet in the declinometer be deflected toward the east, a current will be generated, running from south to north along the upper bar of the rectangle, and back along the lower bar. The current, in turn, acts upon the magnet, checking it in its swing toward the east, so that the paper can receive the entire trace. In addition to the concave mirror, each magnet carries a plane mirror to receive the reflection of a scale attached to the back of a small telescope. ”