Your left hand and right hand are mirror images of each other. There's no way you can position your left hand so that it looks like a right hand. It will only look like a right hand if you look at it in a mirror.

There are molecules like this in chemistry. Molecules that can't be positioned in such a way as to look exactly like their own mirror image. These are called chiral molecules. We talk about them having a handedness because they share this property with our hands.

But what about rubber gloves? You might think that a left handed rubber glove can't be positioned in such a way as to look like a right handed glove. But turning a glove inside out does exactly that!

That's why in chemistry, a chiral molecule that can be manipulated into it's own mirror image, is called a Euclidean rubber glove.

So what about socks? When you first buy a pair of socks, left and right look exactly the same. They don't have this chiral property. But after you've worn them a while and put a hole in with your big toe, they do.

So if you've got a big toe hole in your sock, you can make it more comfortable by turning it inside out. The hole will switch to the other side where your toes are less likely to poke out.

This can make pictures look funny, so manufacturers add a filter to block the infrared and give you a more natural image. Actually the filters don't do a perfect job and if you fire a TV remote control at your camera phone you should see it light up on the screen.

All this means you can have a bit of fun with your old web cam. You can remove the infrared filter then add a visible light filter so your webcam only sees infrared!

There are loads of different makes of webcam but most of them have a bit that looks like this:

It's the lens assembly. The end you can see is the end that sticks out of the webcam. At the other end is the IR filter.

I was able to slice off about 1mm from the end to release the filter using a stanley knife:

Then it just screws back into place.

So now you're letting in the infrared all you have to do is block out the visible. You can buy a special filter for the job, or (thanks to Alby Reid) you can cross two polarising filters because these generally only block out visible light. Try the lenses from a pair of 3D glasses (with ReadD branded glasses you'll need to flip them around in all different combination until you find the one that blocks light. That's because they filter circularly polarised light and are a little more complicated than straight polarisers) Here's my setup:

For a while I wasn't seeing anything, just a black screen. Then I realised all the light in room was from energy saving lightbulbs which give off no infrared. I switched to an old style incandescent bulb and the room lit up!

Here are some weird looking things (click to enlarge):

I think my Mona Lisa might be a fake!

Only the Queen is left when you take away visible light:

And here's my eyeball:

Plants aren't that into infrared:

click to enlarge

http://feeds.feedburner.com/RedditFeedWithAScoreThreshold

1000 won't work for everyone so you can customise the feed from the Yahoo Pipe I built:

http://pipes.yahoo.com/pipes/pipe.info?_id=4a3af06dcba612424a858ea79dd263db

You can also specify the subreddit.

"Features"

It feels a little grand to be calling these features but here we go:

• Links to images have the images embedded into the feed.
• If the link is to an imgur.com html page it embeds the image from that too.
• Links to youtube are embedded.
• The feed has a link to the comments page, the posters page and the subreddit page.

Limitations

The Yahoo Pipe gets its data from the top stories of the day. On the "all" subreddit for example top stories of the day rarely get above 2500. That's not to say stories don't eventually get above that, it's just you have to look at top stores for the week or month etc to see scores that high.

As this pipe only scrapes the top stories for the day you'll start to miss out on stories if you put a value over about 2000. The same goes for subreddits but with a different threshold.

If you'd like a higher threshold option let me know and I'll look into making pipes that get their data from the top week and month stories.

If you subscribe with google reader this becomes relevent:

http://www.google.com/support/reader/bin/answer.py?hl=en&answer=97875

Basically google reader has an algorithm for working out how often to refresh a feed. If the feed is relatively new to the world that interval will be large but will get smaller. And you can manually refresh if you want to.

Which rasher is longer?

Ever since the invention of flat panel monitors and screens, it didn't matter what colour your pixels were, you'd still consume the same amount of power. That's because these screens have a big flat light at the back that's always on. If a pixel wants to show you white it lets all the light through. If it wants to show you black it blocks all the light. Either way, the light behind is still on and still consuming the same power.

On a mobile phone that means the colour of your wallpaper doesn't affect battery life. But all that changed with the introduction of OLED screens (or more commonly AMOLED and Super AMOLED) and a lot of new phones have these. If your phone has an OLED screen keep reading, you might be able to improve the life of you battery.

Why is OLED different?

OLED screens don't have a back light. Instead each pixel is an Organic Light Emitting Diode that makes its own light. That means reducing how many pixels you have on during regular use of your phone can have a big impact on battery life. That doesn't just mean changing your wallpaper. You could also look at alternative apps that have dark themes. For example, I spend a lot of time reading news on my phone and I've switched to an app call NewsRob that has the option of light text on a dark background. Here's NewsRob:

An unanswered question

There seems to be a lot of speculation about just how much battery you can save by changing things like your wallpaper but not much in the way of hard evidence. So I wanted to be a bit more systematic about it and come up with some robust answers. It's not quite scientifically rigorous but I'll tell you my methods and you can judge for yourself. In case you're not interested in the method, the conclusions come first...

Conclusions

Here are some caveats

• These tests were performed on a Nexus S. I can only assume other Super AMOLED phones will have similar results, but it is just that, an assumption.
• The figures for maximum brightness and minimum brightness are exact. For brightnesses in between I calculate power consumption by assuming that it varies linearly with brightness. This may very well not be true.

So how much more power does a white pixel at full brightness use than a black pixel? First of all, a black pixel does use some small amount of power. I'm not sure why. Perhaps it's to keep the pixel in a state of readiness or something like that.

A full brightness white pixel uses 5.8 times more juice than a black pixel:

That doesn't mean you could ever increase your battery life by 5.8 times. That's for 2 reasons. The first is that no one spends all day staring at a fully white screen and because no one would every want to switch to a fully black screen! The second is that the screen isn't the only thing using power.

But what we have got is the extremes and we can use those to calculate the in betweens. For example, if half of your battery was used up by the screen and you were able to, on average, reduce how "on" your pixels were from a half to a quarter you'd reduce battery consumption by:

That's quite a complicated looking equation but it's not really. If you're interested in where it came from you can have a look at what I'm glamorously referring to as Appendix A. But if you're just wondering where the 4.8 comes from, it's the 5.8 from earlier minus 1!

So this shows an 18% saving in this imagined scenario. Not bad! But is it realistic?

To answer that question we need to look at two things:

• How much of the battery is used by the screen.
• By how much you can realistically reduce how bright your pixels are.

The first question depends on how you use your phone. If you spend a lot of time on calls that's what will mostly be using your battery. But if it's email and Angry Birds it'll be your screen that tops the charts. The good news is, you can find out for yourself just how hungry your screen is. Or at least you can on Android. I don't know about iPhone but iPhone screens are backlit anyway. Same for Blackberry.

From the home screen, press menu button, then Settings, then Applications, then Battery use.

Here's mine:

So 41% of my battery was used by the screen in the hour and three quarters prior to this screenshot. This varies quite a bit so I kept track of it for a while and it averaged out at about 40%.

But by how much could I reasonably reduce the average pixel brightness on my phone? By analysing screenshots and monitoring brightness settings we should be able to work it out. Let's look first at changing wallpaper. I've got no idea what the brightness of the average wallpaper is so I'm just going to go with a 50% grey wallpaper for the purposes of this comparison. Here's a screenshot with the grey wallpaper next to another with black wallpaper:

When the grey wallpaper is used the average pixel brightness is 47%. For the black wallpaper it's just 15%.

Screenshots don't take the brightness setting on your phone into account (a white pixel will come out as white in a screenshot even if your brightness is set low). So we need to factor that in as well. I have my brightness set to auto and this gives me on a typical day an average of about 50% full brightness. If you use your phone a lot outside, this value will be higher.

So plugging all this into our equation means that if I spent all day on the home screen I'd save:

The 0.4 comes from the 40% of battery used by the screen. The 0.5 comes from the brightness setting on my phone. The 0.47 and 0.15 come from the average pixel brightness of the screenshots.

Of course I don't spend all my phone time just looking at the home screen. I do spend a lot of time reading news. Here's a comparison between reading an article on Google's official Reader app for Android and reading an article on NewsRob set to night mode:

The average pixel brightness for Goolge's official app is 89%. For NewsRob it's 21%. So while I'm using NewsRob I'm saving:

That's quite a bit of battery!

Another app that could save your battery is Handcent, a replacement for the default SMS app. If you spend a lot of time sending text messages this might be a good idea. You'll need to customise it to get a dark theme but that's pretty easy. Here's Handcent:

Know of any other apps with dark themes? Let us know in the comments.

If you want to work out how much you could save, read though the Method section below where I talk about how I calculated the average brightness.

Method

Calculating white pixel battery use vs. black

To compare white pixel battery use to black pixel use. I just filled the screen with white by looking at a full white image in the galley app full screen and left it like that for 2 hours. I did the same with a full black image.

Some extra steps and precautions:

• Put the phone in airplane mode
• Reboot phone before starting each test
• Prevent the screen from timing out
• Set screen to full brightness

The first two points just standardise the experiments by making sure that other things that might use the battery are minimal. Though this isn't so important because we account for other uses in a later step.

At the end of the two hours I measured the battery level and looked inside the battery app to see what percentage of the battery was used by the screen. Here are the results of that:

It's a simple case of multiplying the columns together to get the actual percentage drop due to the screen. That comes out as:

White pixels: 71.0%

Black pixels: 12.2%

So we know that a full brightness white pixel uses:

times more battery than a black pixel.

Analysing average brightness

First of all you need to take screenshots of your Android. Here's how to do that. Second you need to work out average pixel brightness. To do that I opened the screenshots in PhotoShop, applied an Average Blur filter then used the eye dropper tool to get the colour. Look at the B value of that colour to find the percentage brightness.

Some final tips

All colours are not equal. I read that blue pixels consume more power. I've not tested this but I might for a future post. But if you do want a colourful wallpaper maybe go for a red and green theme.

When I switched from grey to black wallpaper I didn't change the icons at all. But if you install ADW Launcher as your home screen you can install icon themes. Other apps enable you to do this too. So you could save even more by switching to a dark theme with dark icons. Here's ADW Launcher:

There's a great app called Screen Filter that lets you dim the screen even further than Android allows in the settings. Here's Screen Filter:

Any more tips for saving battery? Let us know in the comments.

Appendix A - Formula derivation

Here's how I got to the formula I used to calculate battery saving.

So even when the screen is showing all black pixels some power is used. Lets call that power c. The value of c isn't important because it drops out later.

Max brightness full white screen uses 5.8 times this power or 5.8c.

Assuming power goes linearly with brightness then:

where P is power and L is brightness on a scale of 0 to 1 (substitute those values in to verify).

We can calculate L by multiplying the level of brightness derived from the screenshots, l, and the brightness setting of the phone,b:

So we can calculate the change in power consumption between to screenshot derived brightness levels like this:

Which means the fractional change in power consumption is:

To calculate by how much total battery use is affected just multiply this value by the fraction of the battery used by the screen. In my case that was 40% or 0.4 but lets call it for a giggle. Then the fractional decrease in battery drain would be:

which is the equation I've been using in the post.

Use a Google Apps Account To Authenticate Outgoing Mail From Your Regular Gmail Account

Update 16/01/11: Helpful commenter Ewerton points out you can just hit the tab key to bring up the login prompt. So the below now saves you a grand total on 1 key press! Probably not worth it

I find myself clicking on this a lot:

It brings up this little box from which you can log in to twitter:

In fact, it's rare that I don't want to click on "Sign in". So wouldn't it be great if that log in box was already there and that the cursor was in the username box ready to be typed in.

I've written a greasemonkey script to do just that! It works in firefox with greasemonkey installed and in Chrome. Here it is:

Twitter login greasemonkey script. (clicking the link won't do anything interesting unless you're using Chrome or have greasemonkey installed in firefox)

If you're interested to know the technical details keep reading.

When you click on the sign in button three things happen:

• The sign in link gets the menu-open class added which changes it's appearance
• The login box (signin_menu div) loses the offscreen class. The offscreen class positions the div -9999px from the left!
• The username field gains focus

All the greasemonkey script does is recreate the behaviour when the page loads.

Check out my greasemonkey script for making TfL's Journey planner much easier to use.

Is the second sound higher or lower than the first sound? (let us know in the comments). Play it again if you're not sure.

Ask a few other people to do the same. You'll find that some people hear the second note as higher and some hear it as lower!

(mini update: so far 5 commenters hear the second note as lower and 8 hear it as higher)

That's because it's an audio illusion. And just like an optical illusion an audio illusion can tell us something about the way we perceive the world around us.

The explanation is all to do with resonance and harmonics.

What is resonance?

When you pluck a guitar string the note it produces is the resonating frequency of the string. So you can think or resonance as the tendency of a system (like a tight string) to oscillate at a particular frequency when you put energy in it in the right way.

But it turns out that systems can have more than one resonating frequency. They can have a whole series of harmonics.

What are harmonics?

If you pluck that guitar string again but this time rest your finger gently on it right at the centre you'll hear a new note. This is also a resonating frequency of the string and it's twice as high as the first.

If you then rest one finger a third of the way down and another two thirds or the way down and pluck the string (with your third hand presumably) you'll get another resonating frequency. The pitch of this one will be three times that of the open string.

The points where you rest your fingers are called nodes. The places where, for that resonating frequency there is no movement. You could continue adding nodes and getting new frequencies along the way.

These are called harmonics. The first harmonic, or fundamental harmonic, is what you hear with an open string. The next one up is the second harmonic and so on. Here's what they look like:

Now in reality when you pluck an open string you're actually getting a mixture of all these harmonics but you only hear the fundamental. The other harmonics don't register as distinct notes but instead make the whole sound richer. Here's an illustration of the sound produced by a guitar string being plucked:

You only hear that lowest frequency but the other harmonics are there.

How does all this relate to the audio illusion?

Natural systems like the guitar string or human vocal cords tend to vibrate in this way, they vibrate at a fundamental harmonic and all the other harmonics on top. So our senses have evolved to interpret these mixtures of harmonics as a single tone coming from a single entity.

Here are two notes side by side:

As you can see the second note is lower. And this is exactly what you're hearing when you play the sounds at the top of this post except for one important difference. The fundamental frequency of the second note has been taken away so it looks like this:

That gap is "unnatural" and the way you interpret that depends on how your brain works.

It turns out that the way we perceive pitch isn't just to do with the tones we hear but also the pattern of tones. So for some of us our brains would receive the pattern of frequencies of the second note, ignore that fact that the pattern is broken, and interpret the sound as being lower. In other words your brain is hearing the fundamental harmonic that isn't there.

On the other hand, if you heard the pitch go up, that's because the pattern of frequencies is less important to your brain than the absolute lowest frequency.

Most people are a mixture of the two and depending on how you engineer the two sounds you can get anyone to hear or not hear the missing fundamental.

Did you hear it? Let us know in the comments.

You might also like the optical illusion in this post.

Update: Some interesting insight from Martin Coath who first told me about the effect: "The predisposition to hear one or the other is correlated with a volumetric asymmetry in Hesch'ls Gyrus - ie one of the auditory parts of your brain is bigger on the left or the right. (Schneider, Sluming et al Nature Neuroscience 8, 1241 - 1247, 2005)"

Another update: Awesome commenter sci ran my sounds through a frequency analyser and got this:

I've attempted to anotate this image to show what I think is going on (am I getting it right sci?):

So my original illustrations are a bit off. The sounds have fewer harmonics than I thought. But it does show the missing fundamental which I'm very excited about Thanks sci.

All you need to make a fire tornado is:

A bin made from metal mesh. Something like this.

A lazy susan

The little tin case from a tea light. This sort of thing.

Lighter fluid

A BBQ lighter

Put a little bit of the lighter fluid into the empty tea light. Not too much. Put in less that a millimetre. That way it'll safely burn itself out after a short time.

Put it all together like in the video and light it. Give the whole thing a little spin.

I experimented with different diameters of mesh tube and different containers for the lighter fluid. I discovered:

• A wider mesh is better. I'll explain why later
• A smaller container is better. This produces a much more dramatic change in high when the vortex kicks in.

Why does this happen?

A flame draws air in from around it. That's because it heats the air. Hot air is less dense and so it rises up. Air is drawn in from the sides to fill the space left behind.

In our case the air is drawn in through the mash of the bin. As it passes though it gets pulled around in a circle. It's now got some kinetic energy. When the air is pulled further into the middle, that energy is conserved. It's still going round in a circle but the circle is much smaller so it's orbital speed will increase to keep it's kinetic energy the same. This is the conservation of angular momentum.

So the reason a wider mesh is better is that for the same orbital speed a wider mesh will be travelling faster and imparting more kinetic energy.

I'm not sure why the flames get bigger. Any ideas?

You might also like these giant steel balls you can burn things with.