A cloud chamber simply lets you see traces of ionizing radioation such as alpha and beta particles. What happens in the chamber is that at the bottom the peltiers cool down to at least -18f or below, to supersaturate 99% isopropanyl alcohol. When charged particles pass thru the supersaturated mist of alcohol at the bottom of the chamber, the air gets ionized and the alcohol almost instantly condense and forms small visible tracks. That's pretty much it, you can find further information at Google!!
This is a piece a Fiestaware saucer in my chamber.