Gepard wrote:userjjb wrote:snip>Water vapor is transparent to the naked eye <snip>
Surely not as otherwise we wouldn't see clouds.
Actually water vapor is indeed transparent, what people typically call "steam" (for instance when water boils) is actually not vapor at all, but rather small condensed water droplets. Clouds are made out of these water droplets and so we can see them. If water vapor was opaque we wouldn't be able to see anything at all because the atmosphere contains around 1% water vapor. When you fire a pneumatic the gas in the chamber rapidly expands cooling it down. This causes the water vapor to condense into visible liquid water droplets.