On The modification of clouds
Luke Howard 1802
"There are three simple and distinct modifications in any one of which the aggregate of minute drops called a cloud may be formed, increase to its greatest extent and finally decrease and disappear � but the same aggregate which has been formed in one modification, upon a change in attendant circumstances, may pass into another."
- Cirrus (from Latin for "fiber" or "hair"): "Parallel, flexuous or diverging fibres, extensive in any or in all directions."
- Cumulus (from the Latin for "heap" or "pile"): "Convex or conical heaps, increasing upwards from a horizontal base."
- Stratus (adapted from the Latin stratum for "layer" or "sheet"): "A widely extended continuous horizontal sheet, increasing from below upwards."
- (Cumulo- Cirro- or Stratus-) Nimbus (from the Latin for "cloud"): "The rain cloud. A cloud or system of clouds from which rain is falling.�"
- Cirro-Cumulus: "Small, well defined roundish masses, in close horizontal arrangement or contact."
- Cirro-Stratus: "Horizontal or slightly inclined masses attenuated towards a part or the whole of their circumference, bent downward, or undulated, separate or in groups consisting of small clouds having these characteristics."
- Cumulo-Stratus: "The cirro-stratus blended with the cumulus, and either appearing intermixed with the heaps of the latter or superadding a wide spread structure to its base."
Current definitions
High Clouds (bases > 6 kilometers)
1. Cirrus (Howard, 1803)
2. Cirrocumulus (Howard, 1803)
3. Cirrostratus (Howard, 1803)
Middle Clouds (bases 2 � 6 kilometers)
4. Altocumulus (Renou, 1870)
5. Altostratus (Renou, 1870)
6. Nimbostratus (International Commission for the study of Clouds, 1930)
Low Clouds (bases < 2 kilometers)
7. Stratocumulus (Kaemtz, 1841)
8. Stratus (Howard, 1803)
9. Cumulus (Howard, 1803)
And the final cloud type extending through all ranges of altitudes
10. Cumulonimbus (Weilbach, 1880)
http://www.bom.gov.au/info/clouds/