Deleted. Copy held on local disk - will be posted elsewhere in due course.

A favourite question of smart-alecs at dinner parties is "Why are things in a mirror reversed left to right, but not up and down?". The resulting conversation is as tedious as it is pointless, and gives the questioner a chance to look wise without going through the complex process of learning anything.

This entry approaches the question by providing different explanations for each of people, writing, and directions. In fact, all three are left-right reversed for fundamentally the same reason, but tackling different kinds of objects seperately makes things easier to start with.

People

Suppose that Snow White is looking in a mirror(No, not the magic mirror - just a regular enchantment-free one this time. Imagine that Snow White's government enacted a series of anti-snooping laws or something.). Obviously she sees another maiden as charming and beautiful as herself - lets call her 'Magnolia Drifts'. Snow White is real and Magnolia is just a reflection, but from the point of view of this entry there are three important differences:

• Magnolia is facing the opposite direction to Snow.
• Magnolis is in a different position to Snow.
• Magnolia is left-right reversed, compared to Snow.

This way of looking at Magnolia could be called the standard perspective. However, there is another view:

• Magnolia is front-back (Author's Note: I'm tempted to call this axxehole-cxxt reversed, but that'd be just crude...) reversed, compared to Snow.

This perspective could be called the direct perspective since it is a direct view onto what is really happening. Here's an experiment to help access this perspective.

The Compass Experiment

You'll need a piece of card (about A4 size), a marker pen, scissors, and a wall-mounted mirror:

1. Cut the piece of card into a rough circle. This circle of card is going to become a compass.
2. Decide which way is going to be North. Mark a star in this position.
3. Mark an 'X' at South, an 'O' at West, and a filled 'O' at East.
4. Stand in front of the mirror, holding the compass horizontally so you can see it directly and you can also see its reflection in the mirror, but you cannot see your own reflection in the mirror.
5. Rotate the compass so that North (the star) is pointing towards the mirror. Notice that the reflected compass correctly identifies East and West, but has North and South back to front.
6. Rotate the compass clockwise so that West is pointing towards the mirror. Notice that the reflected compass correctly identifies North and South, but has East and West back to front.
7. Keep playing with the compass and its reflection until you can see the direct perspective.

Which Perspective(Not on sale in all good newsagents)?

There is a third perspective: the weird perspective. Imagine that Snow White is rotated like a table football player. The rotated Snow White will have her arms pointed down and her legs pointed up(And stop trying to sneak a look at her underwear! That's not a very nice way to treat a fairytale princess, is it?) and facing the opposite direction. This rotated Snow White is facing the same way as Magnolia, but is up-down reversed, rather than left-right reversed.

The standard perspective is more natural than the direct or weird perspectives. This is because we frequently see people moving and turning, but reflection is much rarer. So it is more natural to see first that Magnolia is in a different place=and looking in a different direction, and only later see that she is left-right reversed.

Similarly, people rarely rotate like table football players. If you are walking to the shops, and realise you've forgotten your purse, do you:

• Put your hands on the floor, kick your feet into the air, and walk back home on your hands?
• Turn around, keeping your feet on the floor, and walk back home normally?
• Keep going, because you realise the place you left your purse is the shop you're walking to, from the previous visit?

Another factor is that left and right hands are similar, while hands and feet are different. It's interesting to contemplate how, for example, a Beholder(In mythology, a beholder is a floating ball with a single central eye. In some traditions it also has smaller eyes floating on stalks above it, but that's just showing off and, more importantly, ruining the example.) might view a reflection of itself.

Writing

Get yourself another piece of card, and the marker pen you kept from the Compass Experiment above. On the card, write the name of the first person you kissed (The romantically challenged, or plain forgetful, can just write "Fred".). Now, stand opposite your mirror, turn the card around so that the card faces the mirror, and look at the reflection. You'll see that it's been reflected left-to-right, and looks like mirror-writing. So far, so normal. However, this time it's not just a matter of perspective.

The critical step is turning the card round. If you turn the card round normally, then you are rotating it around a vertical access, so the reflection is reflected left-to-right. Instead, try turning the card around a horizontal axis (remember the table football players?) - now when you look at the reflected name, you'll see it's been reflected so that up and down are reversed: for example, a 'p' will have become a 'b'. The manner that the writing is reflected depends on how you rotate the card.

It's possible to view the reversal in other people's reflections in the same way as wriing, for those seeking a Unified Theory of Mirrors. Going back to Snow White above, tell Snow White to face you, with her back to the mirror. Memorise what she looks like. Now tell her to turn around so that she's facing the mirror, and look at Magnolia, her reflection. Magnolia will be left-right reversed, and this is because Snow White will have turned around in the style of a princess, not in the style of a plastic table football player.

Directions

If you have ever tried to give directions to your reflection, you'll probably have found it unresponsive. You may have previously thought that this is because your reflection is a virtual object made up entirely of photons. However, this entry can exclusively reveal that it's actually because your reflection is confused by which directions are reversed, and which are not. Next time, provide it with this handy guide, and revel in the satisfaction of a well-motivated reflection.

Imagine that the mirror is mounted on a South-facing wall - so in order to look into the mirror you have to look North. In the reflected world, North is switched with South, while East, West, up and down, all remain unchanged (remember the compass experiment earlier?). Other directions have their North-South component switched over, but other components unchanged. Left and right are different from normal directions, because they are rotational. Stand up, and face North. Left is East. Turn 90° left to face East. Left is now South.. So, left is actually North->East->South->West->North. Even though left is initially East, and East is not reversed in the mirror, left itself is reversed, because it contains North and South, which are reversed. Meanwhile, the rotational direction that goes North->down->South->up->North is also reversed, and the rotational direction that goes East->down->West->up->East is not reversed.

To check this, lie down on the floor in front of a full length mirror, so that your toes point towards the mirror and your head points away from it. Now, rotate to your left and right and check your reflection as you do so(Looking good!). Notice that whichever way you turn, your reflection is facing the same direction as you. When you are staring at the ceiling, your reflection is also staring at the celing. When you are staring at the floor, your reflection is also aware that sie needs to hoover. You can do the same experiment by standing on top of a reflective surface like a pond, but if you can walk on water you've probably got more important things to do than figure out why reflections are always left-right reversed...