Low in the sky there's the classic cotton wool Cumulus, the Stratus, a layer of "rather dull" cloud, and higher up Cirrus - "a translucent delicate streak as if a watercolour brush has been stroked across the blue".
There were, he announced, only three basic cloud types, and he gave each a Latin name befitting its appearance: cirrus for fiber, cumulus for heap or pile and stratus for layer or sheet.