Thales of Miletus, [11], [61], [68], [208], [210].

theamedes, the, [18].

Thebitius, or Thebit ben Korrah, [117], [236].

Themistius, [71].

Theophrastus, [1], [9], [11].

Thomas Aquinas, [3], [64].

tides, the cause of, [86].

Tycho Brahe, [174], [229].

Variation of the compass, [7], [46], [79], [116], [151]-[163], [166], [167], [180].

variation at the Azores, [4], [154], [156], [167].