I think, if you live with your head in the clouds every now and then, it helps you keep your feet on the ground. And I want to show you why, with the help of some of my favourite types of clouds. Let's start with this one. It's the cirrus cloud, named after the Latin for a lock of hair. It's composed entirely of ice crystals cascading from the upper reaches of the troposphere, and as these ice crystals fall, they pass through different layers with different winds and they speed up and slow down, giving the cloud these brush-stroked appearances, these brush-stroke forms known as fall streaks. And these winds up there can be very, very fierce. They can be 200 miles an hour, 300 miles an hour. These clouds are bombing along, but from all the way down here, they appear to be moving gracefully, slowly, like most clouds. And so to tune into the clouds is to slow down, to calm down. It's like a bit of everyday meditation. Those are common clouds. What about rarer ones, like the lenticularis, the UFO-shaped lenticularis cloud? These clouds form in the region of mountains. When the wind passes, rises to pass over the mountain, it can take on a wave-like path in the lee of the peak, with these clouds hovering at the crest of these invisible standing waves of air, these flying saucer-like forms, and some of the early black-and-white UFO photos are in fact lenticularis clouds. It's true. A little rarer are the fall streak holes. All right? This is when a layer is made up of very, very cold water droplets.