by William Gilbert

“ The declination of a magnetick needle above a terrella is shown by means of several equal iron wires, of the length of a barleycorn, arranged along a meridian. The wires on the æquator are directed by the virtue of the stone toward the poles, and lie down upon its body along the plane of its horizon. The nearer they are brought to the poles, the more they are raised up by their versatory nature. At the poles themselves they point perpendicularly toward the very centre. ”

“ Here we have the level position of the magnetick needle on the æquator of the earth and the stone, at A and B, and its perpendicular position at C, D, the poles; whilst at the places midway between, at a distance of 45 degrees, the crosses of the needle dip toward the south, but the cusps just as much toward the north. Of which thing the reason will become clear from the demonstrations that follow.
* Diagram of the rotation and declination of a terrella
conforming to the globe of the earth, for a
latitude of 50 degrees north. ”

“ But iron spikes, if they are of more than a due length, are not raised straight up except on a vigorous stone.
The page and line references given in these notes are in all cases first to the Latin edition of 1600, and secondly to the English edition of 1900. 233 ↑ Page 190, line 14. Page 190, line 19. declinans in Borealibus.—Dipping as it does in northern regions; that is, with the north-seeking or true-south pole downward. ”