Mr. Howard had not the advantages of a balloon to assist his observations. He has noticed that during rain and before the arrival of the denser and lower clouds, or through their interstices, there exists, at a greater height, a thin light veil or a hazy appearance. When this has considerably increased, the lower clouds are seen to spread till they unite in all points and form one uniform sheet. The rain then commences, and the lower clouds arriving from the windward, move under this sheet and are successively lost in it. When the latter cease to arrive, or when the sheet breaks, letting through the sun-beams, every one’s experience teaches him to expect that the rain will abate or leave off. But there often follows an immediate and great addition to the quantity of cloud. At the same time the darkness becomes less, because the arrangement, which now returns, gives free passage to the rays of light; the lower broken clouds rise into cumuli, and the upper sheets put on the various forms of the cumulo-stratus, sometimes passing to the cirro-cumulus. The various phenomena of the rain-cloud are best seen in a distant shower. If the cumulus be the only cloud at first visible, its upper part is seen to become tufted with cirri. Several adjacent clouds also approach and unite at its side. The cirri increase, extending upwards and sideways, after which the shower is seen to commence. At other times, the cirro-stratus is first formed above the cumulus, and their sudden union is attended with the production of cirri and rain. In either case the cirri spring up in proportion to the quantity of rain falling, and give the cloud a character by which it is easily known at great distances, and which has long been called by the name of _nimbus_. When one of these arrives hastily with the wind, it brings but little rain, and frequently some hail or driven snow. Since rain may be produced and continue to fall from the slightest obscuration of the sky by the nimbus, while a cumulus or a cumulo-stratus, of a very dark and threatening aspect, passes on without discharging any until some change of state takes place; it would seem as if nature had destined the latter as reservoirs, in which water is collected from extensive regions of the air for occasionally irrigating particular spots in dry seasons; and by means of which it is arrested, at times, in its descent in wet ones. Although the nimbus is one of the least beautiful of clouds, it is, nevertheless, now and then adorned by the splendid colouring of the rainbow, which can only be seen in perfection when the dark surface of this cloud forms for it a background.