Another important factor to consider is that water vapour needs something to condense onto. Floating in the air are millions of minute salt, dust and smoke particles known as condensation nuclei which enable condensation to take place when the air is just saturated. In 1803 a retail chemist and amateur meteorologist called Luke Howard proposed a system which has subsequently become the basis of the present international classification. They had ejected dust high up into the atmosphere, thereby increasing the amount of condensation nuclei, and producing spectacular cloud formations and sunsets. The cloud types are split into three groups according to the height of their base above mean sea level.
All heights given are approximate above sea level in mid-latitudes.
If observing from a hill top or mountain site, the range of bases will accordingly be lower. White on its sunlit parts but with darker undersides. This cloud appears in the form of detached heaps. Shallow cumulus may appear quite ragged, especially in strong winds, but well formed clouds have flattened bases and sharp outlines. White upper parts with dark, threatening undersides.