2], the anomalies of the motion of the Earth's axis are
described, so far as the observations of the ancients down to our own times
admit; but there are still needed more and exact observations for anyone to
establish aught certain about the anomaly of the motion of the
praecessions, and at the same time that also of the obliquity of the
Zodiack. For ever since the time at which, by means of various
observations, this anomaly was first observed, we have only arrived at half
a period of the obliquity. So that all the more all these matters about the
unequal motion both of the praecession and of the obliquity are uncertain
and not well known: wherefore neither can we ourselves assign any natural
causes for it, and establish it for certain. Wherefore also do we to our
reasonings and experiments magnetical here set an end and period.[253]

[Illustration]

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INDEX.

Abano, Pietro di (Apponensis or Apianus), 2.
Abbas, Hali ('Ali ibn Al 'Abb[=a]s, _Al Majusi_, 2, 6.
Abohalis, 47. _See also_ Avicenna.
_aciarium_ or _acies_, also _aciare_, 18, 23, 33, 36.
Acosta, Josephus, 5.
adamant, 11.
aequator, the magnetick, 13, 79.
Aetius Amidenus, 2.
Affaytatus, Fortunius, 6.
agate, non electrick, 51, 53.
Agricola, Georgius, 2, 3, 10, 19, 26, 111, 112.
Agrippa, H. Cornelius, 3.
_aimant_, 11.
Albategnius (Muhammad ibn J[=a]bir, _Al-Batt[=a]ni_, 237.
Albertus Magnus, 2, 7, 18, 111.
Alexander Aphrodiseus, 3, 48, 92.
Alexandria, Hero of, 58.
Alfonso, Diego, 178.
Alfonsus the Wise (Alphonsus X.), 237.
Amalfians said to have first constructed the compass, 4.
Amatus Lusitanus, 2.
amber, 47, 49-60, 85, 112, 116.
amethyst, electrical properties of, 48.
amianth, 11.
Amidenus, Aetius, 2.
amphitane, 111.
Anatolismus, or Northeasting, 167.
Anaxagoras, 61, 208.
Andrea Doria (Admiral), 4.
Antonius de Fantis, 107.
Antonius Musa Brasavolus, 2.
Antony, the denarius of, 110.
Apianus. _See_ Abano.
Apponensis. _See_ Abano.
Aquinas, Thomas, 3, 64.
Aractensis, Mahometes, 234, 237.
Archelaus, 208.
Ardoynis, Santes de, 2.
Arias Montanus, 4.
Aristarchus, 214, 237.
Aristotle:
_De Anima_, 1, 11, 61, 210.
_De Coelo_, 226, 232.
_De Mirabilibus Auscultationibus_, 22.
_Meteorologica_, 35, 39.
on material of the metals, 19, 20.
on the element of earth, 43.
on motions, 45, 219, 225.