<P> The origin of the term cloud can be found in the old English clud or clod, meaning a hill or a mass of rock . Around the beginning of the 13th century, it was extended as a metaphor to include rain clouds as masses of evaporated water in the sky because of the similarity in appearance between a mass of rock and a cumulus heap cloud . Over time, the metaphoric term replaced the original old English weolcan to refer to clouds in general . </P> <P> Ancient cloud studies were not made in isolation, but were observed in combination with other weather elements and even other natural sciences . In about 340 BC the Greek philosopher Aristotle wrote Meteorologica, a work which represented the sum of knowledge of the time about natural science, including weather and climate . For the first time, precipitation and the clouds from which precipitation fell were called meteors, which originate from the Greek word meteoros, meaning' high in the sky' . From that word came the modern term meteorology, the study of clouds and weather . Meteorologica was based on intuition and simple observation, but not on what is now considered the scientific method . Nevertheless, it was the first known work that attempted to treat a broad range of meteorological topics . </P> <P> After centuries of speculative theories about the formation and behavior of clouds, the first truly scientific studies were undertaken by Luke Howard in England and Jean - Baptiste Lamarck in France . Howard was a methodical observer with a strong grounding in the Latin language and used his background to classify the various tropospheric cloud types during 1802 . He believed that the changing cloud forms in the sky could unlock the key to weather forecasting . Lamarck had worked independently on cloud classification the same year and had come up with a different naming scheme that failed to make an impression even in his home country of France because it used unusual French names for cloud types . His system of nomenclature included twelve categories of clouds, with such names as (translated from French) hazy clouds, dappled clouds and broom - like clouds . By contrast, Howard used universally accepted Latin, which caught on quickly after it was published in 1803 . As a sign of the popularity of the naming scheme, the German dramatist and poet Johann Wolfgang von Goethe composed four poems about clouds, dedicating them to Howard . An elaboration of Howard's system was eventually formally adopted by the International Meteorological Conference in 1891 . This system covered only the tropospheric cloud types, but the discovery of clouds above the troposphere during the late 19th . century eventually led to the creation separate classification schemes for these very high clouds . </P> <P> Tropospheric classification is based on a hierarchy of categories with physical forms and altitude levels at the top . These are cross-classified into a total of ten genus types, most of which can be divided into species and further subdivided into varieties which are at the bottom of the hierarchy . </P>

How high are rain clouds from the ground