8848

Alex Bellos discusses how the Incans used knots in string (Quipu) to record numbers.Check out Brilliant (get 20% off their premium service): https://brillian...

Brady - who makes these videos - is back from a holiday to Mt Everest. So here's a video about the height of the mountain before we return to our usual stuff (we promise!).

Some of Brady's photos can be seen at http://periodicvideos.blogspot.co.uk/2012/05/some-everest-photos.html