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From: ark@rabbit.UUCP (Andrew Koenig)
Newsgroups: net.philosophy
Subject: Re: Why do mirrors reverse left & right, not up & down?
Message-ID: <2471@rabbit.UUCP>
Date: Thu, 2-Feb-84 22:13:51 EST
Article-I.D.: rabbit.2471
Posted: Thu Feb  2 22:13:51 1984
Date-Received: Wed, 8-Feb-84 01:50:55 EST
References: <537@bbncca.ARPA>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 26

This is a trick question.  Defining terms carefully makes
the problem go away.

Imagine yourself standing in front of a full-length mirror.
The reflection of your right hand is nearest the right edge
of the mirror, and the reflection of your left hand is nearest
the left edge.  The reflection of your head is nearest the
top edge, and the reflection of your feet is nearest the bottom.

In what way, then, can a mirror be said to reverse left and right,
any more than it reverses top and bottom?

Well, now, you may say, suppose there's a person standing behind you.
Her right hand is also nearest the right edge of the mirror and
her left hand is nearest the left edge.  If you turn around to
look at her, though, her right hand will be on your left and her
left hand will be on your right.  In that sense, what you see when
you look directly at her is reversed left for right compared to what
you see in the mirror.

However, that has nothing to do with the mirror.  Rather, it has to do
with what you did when you turned around to look directly at her.  You
turned around a vertical axis.  If instead you had turned around a horizontal
axis (by standing on your head), her left hand would still be nearest
to your left hand and her right hand would still be nearest your right hand.
Her head, though, would now be near your feet and her feet near your head.