§ 3. I know not if the reader will think at first that questions like these are easily answered. So far from it, I rather believe that some of the mysteries of the clouds never will be understood by us at all. "Knowest thou the balancings of the clouds?" Is the answer ever to be one of pride? "The wondrous works of Him which is perfect in knowledge?" Is _our_ knowledge ever to be so? It is one of the most discouraging consequences of the varied character of this work of mine, that I am wholly unable to take note of the advance of modern science. What has conclusively been discovered or observed about clouds, I know not; but by the chance inquiry possible to me I find no book which fairly states the difficulties of accounting for even the ordinary aspects of the sky. I shall, therefore, be able in this section to do little more than suggest inquiries to the reader, putting the subject in a clear form for him. All men accustomed to investigation will confirm me in saying that it is a great step when we are personally quite certain what we do _not_ know. § 4. First, then, I believe we do not know what makes clouds float. Clouds are water, in some fine form or another; but water is heavier than air, and the finest form you can give a heavy thing will not make it float in a light thing. _On_ it, yes; as a boat: but _in_ it, no. Clouds are not boats, nor boat-shaped, and they float in the air, not on the top of it. "Nay, but though unlike boats, may they not be like feathers? If out of quill substance there may be constructed eider-down, and out of vegetable tissue, thistle-down, both buoyant enough for a time, surely of water-tissue may be constructed also water-down, which will be buoyant enough for all cloudy purposes." Not so. Throw out your eider plumage in a calm day, and it will all come settling to the ground: slowly indeed, to aspect; but practically so fast that all our finest clouds would be here in a heap about our ears in an hour or two, if they were only made of water-feathers. "But may they not be quill-feathers, and have air inside them? May not all their particles be minute little balloons?" A balloon only floats when the air inside it is either specifically, or by heating, lighter than the air it floats in. If the cloud-feathers had warm air inside their quills, a cloud would be warmer than the air about it, which it is not (I believe). And if the cloud-feathers had hydrogen inside their quills, a cloud would be unwholesome for breathing, which it is not--at least so it seems to me. "But may they not have nothing inside their quills?" Then they would rise, as bubbles do through water, just as certainly as, if they were solid feathers, they would fall. All our clouds would go up to the top of the air, and swim in eddies of cloud-foam.