Re: Fabulous Adventures In Coding (Eric Lippert)

From: John Ford (zjcf_at_DawnAndJohn.net)
Date: 02/16/04 

Date: Sun, 15 Feb 2004 19:22:54 -0600

On 2/13/2004 12:50 AM Al Dunbar [MS-MVP] wrote:

> "Richard Cornford" <Richard@litotes.demon.co.uk> wrote in message
> news:c0haec$pd1$1$8302bc10@news.demon.co.uk...
>
>>"Al Dunbar [MS-MVP]" <alan-no-drub-spam@hotmail.com> wrote in message
>>news:eQOj9sS8DHA.1040@TK2MSFTNGP10.phx.gbl...
>><snip>
>>
>>>But seriously, now, can Eric tell us why things seen in a
>>>mirror are reversed side-to-side but not top-to-bottom?
<snip>
> What, did nobody point out that this defect all mirrors have can be easily
> fixed? All you have to do is turn out the light, and the mirror will no
> longer reverse things any which way.
>
> /Al

Forgive my late entry into this foray. I humbly (OK, not so humbly)
submit that the mirror does not reverse anything. Up is still up, right
is still right, etc.. Our expectation is backward, because we most
commonly turn around to see something that is behind us. When we do
that, WE have reversed OUR right and left. Since that's what we're used
to, we assume that a mirror reverses the image. But it only shows the
reverse of what we expect.

When two people face each other and one says "move to the right", you
must know whose "right", because one of you is reversed. If you both
face the same direction and see each other in a mirror, there is no
right/left issue. If we were accustomed to bending over backward to look
behind us (thus reversing up and down), then when the person you're
looking at says "move to the right", it's the same direction for both of
you.

The concept of up and down is not nearly as ambiguous as right and left
in our day-to-day lives, thanks mainly to gravity. Thus, when we arrange
ourselves and a mirror such that up and down might appear reversed, we
intuitively know that it is either us or the object, not the object's
image, that is reversed from normal. 

--
jcf

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