Observers have assumed that the whole explanation of the fantastic shapes taken by clouds is founded on the process of formation; but Dr. Aitken has pointed out that ripple-marked clouds, for instance, have been clouds of decay. When what is called a cirro-stratus cloud--mackerel-like against the blue sky--is carefully observed in fine weather, it will be found that it frequently changes the ripple-marked cirrus in the process of decay to vanishing. Where the cloud is thin enough to be broken through by the clear air that is drawn in between the eddies, the ripple markings get nearer and nearer the centre, as the cloud decays. And, at last, when nearly dissolved, these markings are extended quite across the cloud. Whether, then, we consider the cases of clouds gradually melting away back into their original state of blue water-vapour, or the constant fine raining from clouds and re-formation by evaporation, or the transformation of such clouds as the cirro-stratus into the ripple-marked cirrus, we are forced to the conclusion that in clouds there is not always development, but sometimes degeneration; not always formation, but sometimes decay. CHAPTER XI IT ALWAYS RAINS All are familiar with the answer given by the native of Skye to the irate tourist on that island, who, for the sixth day drenched, asked the question: "Does it always rain here?" "Na!" answered the workman, without at all understanding the joke; "feiles it snaas" (sometimes it snows). Yet, strange to say, the tourist's question has been answered in the affirmative in every place where a cloud is overhead, visible or invisible. Whenever a cloud is formed, it begins to rain; and the drops shower down in immense numbers, though most minute in size--"the playful fancies of the mighty sky." No doubt it is only in certain circumstances that these drops are attracted together so as to form large drops, which fall to the earth in genial showers to refresh the thirsty soil, or in a terrible deluge to cause great destruction. But when the temperature and pressure are not suitable for the formation of what we commonly know as the rain, the fine drops fall into the air under the cloud, where they immediately evaporate from their dust free-surfaces, if the air is dry and warm. This is, in other words, the decay of clouds. It is a curious fact that objects in a fog may not be wetted, when the number of water-particles is great. It seems that these water-particles all evaporate so quickly that even one's hand or face is not sensible of being wetted. The particles are minutely small; and they may evaporate even before reaching the warm skin, by reason of the heated air over the skin. There is a peculiarly warm sensation in the centre of a cumulus cloud, especially when it is not dense. A glow of heat seems to radiate from all points. Yet the face and hands are quite dry, and exposed objects are not wetted; but it is really _always raining_. That is a curious discovery.