The distribution of light and shade in clouds is most striking. The watery particles of which they are composed, yielding constantly to changes in temperature and moisture, are always changing; so that a most beautiful cloud may alter in figure and appearance in an instant of time; the light parts may suddenly become dark, and those that were shaded may all at once glow in the rays of the sun. Again, the appearance of a cloud, with respect to the sun, may entirely alter its character. The same cloud, to one observer, may appear entirely in shade, to another tipped with silver; to a third it may present brilliant points and various degrees of shade, or one of its edges only may appear illuminated; sometimes the middle parts may appear in shadow, while the margin may be partially luminous, rendering the middle parts all the more obscure by the contrast. A wonderful variety may also be produced by the shadow of one cloud falling upon another. The accompanying sketch furnishes an example of this. Sometimes the whole of a cloud projects a shadow through the air upon some other far distant cloud, and this again upon another, until at length it reaches the ground. The shadows of moving clouds may often be traced upon the ground, and they contribute greatly to modify the appearance of the landscape. A large number of small flickering clouds produce broken lights and shades which have an unpleasant jarring effect; but when the clouds are massive, or properly distributed, the shadows often produce a high degree of repose. [Picture: Shadows of clouds]