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                               LETTERS

                                  ON

                            NATURAL MAGIC,

                             ADDRESSED TO

                        SIR WALTER SCOTT, BART.

                                  BY

                   SIR DAVID BREWSTER, LL.D., F.R.S.

      [Illustration: Three figures on hill-top saluting sunrise]

                           SEVENTH EDITION.

                                LONDON:
                WILLIAM TEGG AND Co., 85, QUEEN STREET.
                              CHEAPSIDE.
                                 1856.




CONTENTS.


  LETTER I.

  Extent and interest of the subject--Science employed by
  ancient governments to deceive and enslave their subjects--Influence
  of the supernatural upon ignorant minds--Means
  employed by the ancient magicians to establish
  their authority--Derived from a knowledge of the phenomena
  of Nature--From the influence of narcotic drugs
  upon the victims of their delusion--From every branch of
  science--Acoustics--Hydrostatics--Mechanics--Optics--M.
  Salverte’s work on the occult sciences--Object of
  the following letters                                  Page 1


  LETTER II.

  The eye the most important of our organs--Popular description
  of it--The eye is the most fertile source of mental
  illusions--Disappearance of objects when their images fall
  upon the base of the optic nerve--Disappearance of objects
  when seen obliquely--Deceptions arising from viewing
  objects in a faint light--Luminous figures created by
  pressure on the eye, either from external causes or from
  the fulness of the blood-vessels--Ocular spectra or accidental
  colours--Remarkable effects produced by intense
  light--Influence of the imagination in viewing these
  spectra--Remarkable illusion produced by this affection
  of the eye--Duration of impressions of light on the
  eye--Thaumatrope--Improvements upon it suggested--Disappearance
  of halves of objects or