MR. CLAYDEN'S work will be a standard one for all students of clouds. When the now international classification was first proposed by the late Ralph Abercromby and the present writer, our purpose was to devise a classification for common use at all meteorological stations and in all the navies of the world. It is evident that such a classification must be simple and practicable. A great number of forms must lead to constant errors when used by ordinary observers. Therefore we only proposed the ten types given now in the international cloud atlas.