The Collaborative International Dictionary of English v.0.48:

Looking-glass \Look"ing-glass`\, n.
   A mirror made of glass on which has been placed a backing of
   some reflecting substance, as quicksilver.
   [1913 Webster]

         There is none so homely but loves a looking-glass.
                                                  --South.
   [1913 Webster]

The Devil's Dictionary (1881-1906):

LOOKING-GLASS, n.  A vitreous plane upon which to display a fleeting
show for man's disillusion given.
    The King of Manchuria had a magic looking-glass, whereon whoso
looked saw, not his own image, but only that of the king.  A certain
courtier who had long enjoyed the king's favor and was thereby
enriched beyond any other subject of the realm, said to the king:
"Give me, I pray, thy wonderful mirror, so that when absent out of
thine august presence I may yet do homage before thy visible shadow,
prostrating myself night and morning in the glory of thy benign
countenance, as which nothing has so divine splendor, O Noonday Sun of
the Universe!"
    Please with the speech, the king commanded that the mirror be
conveyed to the courtier's palace; but after, having gone thither
without apprisal, he found it in an apartment where was naught but
idle lumber.  And the mirror was dimmed with dust and overlaced with
cobwebs.  This so angered him that he fisted it hard, shattering the
glass, and was sorely hurt.  Enraged all the more by this mischance,
he commanded that the ungrateful courtier be thrown into prison, and
that the glass be repaired and taken back to his own palace; and this
was done.  But when the king looked again on the mirror he saw not his
image as before, but only the figure of a crowned ass, having a bloody
bandage on one of its hinder hooves -- as the artificers and all who
had looked upon it had before discerned but feared to report.  Taught
wisdom and charity, the king restored his courtier to liberty, had the
mirror set into the back of the throne and reigned many years with
justice and humility; and one day when he fell asleep in death while
on the throne, the whole court saw in the mirror the luminous figure
of an angel, which remains to this day.