William Gilbert,
On the Magnet — Book V. Chap. 3…
(1900)
“ The rim of the cavity represents a meridional circle, to which corresponds some meridian circle of the terrella, since the poles on both sides are within the circumference of the rim itself. These things clearly always happen on the same plan on the earth itself when there is no variation ”
William Gilbert,
On the Magnet — Book V. Chap. 3…
(1900)
“ Let the quadrant be near the limb, or have its centre on the limb itself, and let the versorium be very short, so as not to touch the terrella, because with a versorium that is longer or more remote, there is some error; for it has a motion truly proportionate to the terrella only on the surface of the terrella. ”
