The theory of light / by Thomas Preston.

  • Preston, Thomas.
Date:
1901
Catalogue details

Licence: In copyright

Credit: The theory of light / by Thomas Preston. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    Although the work of Alhazen may have been founded on that of Ptolemy, yet he made such a decided advance in the theory, that for five hundred years or more he was recognised in Europe as the chief authority on the subject. 10. Vitellio.—In 1270 Vitello or Vitellio, a native of Poland, drew up a treatise on optics ^ less prolix and more methodical than that of Alhazen on which it was founded.^ Vitellio attributed the twinkling of the stars to the motion of the air in which the light is refracted, and he remarked that the twinkling is increased when they are viewed through water in gentle motion. He also compiled a table of the angles of incidence and refraction of light at the surface of water and glass, of much greater accuracy than that previously given by Ptolemy. 11. Rogep Bacon.—Contemporary with Vitellio was our country- man Roger Bacon, a man of extraordinary genius, who wrote on almost every branch of science, yet notwithstanding the pains he took with the subject of optics, he does not appear to have made any advance in the theory which Alhazen had already laid down before him. Great as Bacon undoubtedly was, he was far from being free from the prejudices of his predecessors and contemporaries. Some of the wildest and most absurd of the speculations of the ancients had the sanction of his approbation and authority. The invention of the magic-lantern has been attributed to Bacon, but it has been much disputed whether he was acquainted with tele- scopes. Certainly if he was unacquainted with spectacles, telescopes, and microscopes, he anticipated their invention in language more than prophetic.^ ^ Published by Risner in 1572, with the work of Alhazen translated from the Arabic, under the title Thesaurus Opticoe-, Bas. 1572. ^ Vitellio is said to have at first denied that he had any knowledge of the works of Alhazen, but he afterwards retracted this denial and acknowledged himself a disciple of the Arabian philosopher. ^ He says : If the letters of a book, or any minute object be viewed through the lesser segment of a glass sphere or crystal, whose plane base is laid upon them, they will appear far better and larger . . . and therefore this instrument is useful to old men, and to those who have weak eyes ; for they may see the smallest letters sufficiently magnified. And again : '' Greater things than these may be performed by refracted vision. For it is easy to understand by the canons above mentioned, that the greatest things may appear exceedingly small, and on the contrary ; also that the most remote objects may appear just at hand, and on the contrary. . . . And thus from an incredible distance we may read the smallest letters. . . . And thus a boy may appear to be a giant and a man as big as a mountain. ... So also the sun, moon, and stars may be made to descend hither in appearance . . . and many things of like sort which would astonish unskilful persons {Opus Majus, Jebb's edition, p. 377).