Note 89 — Chapter V · Progress of the Arts in the Middle Ages.

If I might take the liberty of criticising an author who has given a very interesting view of the period in question (Mahometanism Unveiled, by the Rev. Charles Forster, 1829), I would remark, that in his work this caution is perhaps too little observed. Thus, he says, in speaking of Alhazen (vol. ii. p. 270), “the theory of the telescope may be found in the work of this astronomer;” and of another, “the uses of magnifying glasses and telescopes, and the principle of their construction, are explained in the Great Work of (Roger) Bacon, with a truth and clearness which have commanded universal admiration.” Such phrases would be much too strong, even if used respecting the optical doctrines of Kepler, which were yet incomparably more true and clear than those of Bacon. To employ such language, in such cases, is to deprive such terms as theory and principle of all meaning.