The French naturalist Jean Lamarck (1744–1829) proposed the first system for classifying clouds in 1802. His work, however, did not receive wide acclaim. A year later the Englishman Luke Howard (1772–1864) developed a cloud classification system that has been generally accepted and is still used today. Clouds are distinguished by their general appearance (“heap clouds” and “layer clouds”) and by their height above the ground. Latin names and prefixes are used to describe these characteristics. The shape names are cirrus (curly or fibrous), stratus (layered), and cumulus (lumpy or piled). The prefixes denoting height are cirro (high clouds with bases above 20,000 feet [6,096 meters]) and alto (mid-level clouds from 6,500 to 20,000 feet [2,000 to 6,096 meters]). There is no prefix for low clouds. Nimbo or nimbus is also added as a name or prefix to indicate that the cloud produces precipitation.