## Here’s the explanation!

by Matthew Cobb

Here’s the explanation of the Mephisto illusion I posted earlier today… Cunning, eh?

1. Damien
Posted October 26, 2017 at 1:36 pm | Permalink

Does he really give the explanation ?

If so I didn’t understand it.

• Janet
Posted October 26, 2017 at 1:44 pm | Permalink

I don’t either!

• infiniteimprobabilit
Posted October 26, 2017 at 7:27 pm | Permalink

The two spirals are opposite-handed – one’s left-handed, one’s tight-handed – and fixed together.

Everybody instinctively assumed the spirals were both the same chirality.

cr

2. sshort
Posted October 26, 2017 at 1:49 pm | Permalink

Ah… chirality strikes again! I didn’t notice that before. I don’t have the math to explain how this works for the illusion, but it must be rather central.

• sshort
Posted October 26, 2017 at 1:51 pm | Permalink

Is it something like phase-shifting?

3. busterggi
Posted October 26, 2017 at 1:56 pm | Permalink

You mean it wasn’t magic?

• sshort
Posted October 26, 2017 at 4:34 pm | Permalink

ha! what i mean is, he said they are wound differently. one right-handed and one left. I suspect that contributes to the illusion in a way two similar-handed coils would not. any topologists around here?

• infiniteimprobabilit
Posted October 26, 2017 at 7:29 pm | Permalink

Don’t need much topology. They’re opposite-handed. So as they both rotate the same way, they seem to be ‘screwing’ in different directions.

cr

4. Frank Bath
Posted October 26, 2017 at 3:26 pm | Permalink

I think he has to turning it in the back of his hand. So a conjuring trick. Otherwise I’m stumped.

5. Diane G.
Posted October 26, 2017 at 6:19 pm | Permalink

Sigh! I mean, sub.

6. mordacious1
Posted October 26, 2017 at 7:04 pm | Permalink

So klar wie Schlamm…

7. b
Posted October 26, 2017 at 7:05 pm | Permalink

i think that the twist is held between the fingers and thumb in such a way that when pulling apart a force is induced that rotates the whole thing

• bascule
Posted October 26, 2017 at 7:06 pm | Permalink

so much for autofill in firefox!

bascule

8. infiniteimprobabilit
Posted October 26, 2017 at 7:34 pm | Permalink

They’re fixed together but opposite-handed.

So as they both rotate the same way, they seem to be ‘screwing’ in opposite directions.

NOBODY in the last post thought of that (I didn’t). Everybody assumed without even thinking about it that both spirals were the same chirality (e.g. both ‘right-handed’).

In fact the guy says it at 6 seconds in to this video and I still missed it till I saw the big welded-together sample at the end.

Once you realise what it is, it’s blindingly obvious to anyone familiar with screw threads, at least.

What a diabolically cunning trick.

cr

9. Michael Fisher
Posted October 26, 2017 at 10:08 pm | Permalink

THIS is a video demonstration of the principle behind the Mephisto Spiral that everybody will understand:

• Diane G.
Posted October 26, 2017 at 11:06 pm | Permalink

That is much clearer, thanks.

10. Melanie
Posted October 26, 2017 at 10:19 pm | Permalink

I feel so stupid. Tell me if this is it: It’s his hands that are moving back and forth – not the spiral?

• Posted October 27, 2017 at 1:09 am | Permalink

yeah, the hand just slides along the coil, it doesn’t grip and pull, which is what people naturally assume.

The operator should take care to obscure the ens of the coils, as soon as observers focus on them the game is up.

11. Charles Minus
Posted October 27, 2017 at 12:27 am | Permalink

Can we give it up for Time Rowett, the presenter here? His Grand Illusions channel on YouTube is responsible for millions of hours of lost production hours due to his charming presentation of clever toys and gimmicks.