The first six books of the elements of Euclid, in which coloured diagrams and symbols are used instead of letters for the greater ease of learners (1847)
Byrne, Oliver, Whittingham, Charles, 1795-1876, Chiswick Press · London : William Pickering · leaf 104
IV. Right lines are faid to be equallydiftant from the centre of a circlewhen the perpendiculars drawn tothem from the centre are equal. … 72 DEFINITIONS.
Euclid's Elements · Geometry
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