"When time came for the shepherds to hold their customary
assembly in order to prepare their monthly report to the king
about the state of the flocks, he came too, wearing this ring.
While he was sitting with the others, it chanced that he moved
the collet of the ring around toward himself into the inside of
his hand; having done this, he disappeared from the sight of
those who were sitting beside him, and they discussed of him as
of someone who had left. And he wondered and once again feeling
for the ring, he turned the collet outwards and, by turning it,
reappeared. Reflecting upon this, he put the ring to the test
to see if it indeed had such power, and he came to this
conclusion that, by turning the collet inwards, he became
invisible, outwards, visible. Having perceived this, he at
once managed for himself to become one of the envoys to the
king; upon arrival, having seduced his wife, with her help,
he laid a hand on the king, murdered him and took hold of the
leadership."
[ The Republic, by Plato, translated by James Adam ]