Ignore the fist minute or so if you like (though it's not completely superfluous). This is a great, simple explanation...from the 1930s. Visually it was simple because it had to be, and yet it is crystal clear. Today we would make this in all sorts of 3D with glitter and sound effects, and bullet points, and we'd shorten it to about 45 seconds. We can learn a lot about simple explanations of complex processes by looking to the past, a time before computers. (Thanks to everyone who sent me this link -- cheers for that!).