Note 17 — THE STORM-CLOUD OF THE NINETEENTH CENTURY.

'Finely comminuted water or ice.'

My impression that these clouds were glacial was at once confirmed by a member of my audience, Dr. John Rae, in conversation after the lecture, in which he communicated to me the perfectly definite observations which he has had the kindness to set down with their dates for me, in the following letter:—

"4, Addison Gardens, Kensington, 4th Feb., 1884.

Dear Sir,—I have looked up my old journal of thirty years ago, written in pencil because it was impossible to keep ink unfrozen in the snow-hut in which I passed the winter of 1853-4, at Repulse Bay, on the Arctic Circle.[A]

On the 1st of February, 1854, I find the following:—

'A beautiful appearance of some cirrus clouds near the sun, the central part of the cloud being of a fine pink or red, then green, and pink fringe. This continued for about a quarter of an hour. The same was observed on the 27th of the month, but not so bright. Distance of clouds from sun, from 3° to 6°.'

On the 1st February the temperature was 38° below zero, and on the 27th February 26° below.

'On the 23d and 30th (of March) the same splendid appearance of clouds as mentioned in last month's journal was observed. On the first of these days, about 10.30 a.m., it was extremely beautiful. The clouds were about 8° or 10° from the sun, below him and slightly to the eastward,—having a green fringe all round, then pink; the center part at first green, and then pink or red.'

The temperature was 21° below zero, Fahrenheit.

There may have been other colors—blue, perhaps—but I merely noted the most prominent; and what I call green may have been bluish, although I do not mention this last color in my notes.

From the lowness of the temperature at the time, the clouds must have been frozen moisture.

The phenomenon is by no means common, even in the Arctic zone.

The second beautiful cloud-picture shown this afternoon brought so visibly to my memory the appearance seen by me as above described, that I could not avoid remarking upon it.

Believe me very truly yours, John Rae." (M.D., F.R.S.)

Now this letter enables me to leave the elements of your problem for you in very clear terms.

Your sky—altogether—may be composed of one or more of four things:—

Molecules of water in warm weather. Molecules of ice in cold weather. Molecules of water-vapor in warm weather. Molecules of ice-vapor in cold weather.

But of the size, distances, or modes of attraction between these different kinds of particles, I find no definite information anywhere, except the somewhat vague statement by Sir William Thomson, that "if a drop of water could be magnified so as to be as large as the earth, and have a diameter of eight thousand miles, then a molecule of this water in it would appear somewhat larger than a shot." (What kind of shot?) "and somewhat smaller than a cricket-ball"!

And as I finally review the common accounts given of cloud formation, I find it quite hopeless for the general reader to deal with the quantity of points which have to be kept in mind and severally valued, before he can account for any given phenomena. I have myself, in many of the passages of 'Modern Painters' before referred to, conceived of cloud too narrowly as always produced by cold, whereas the temperature of a cloud must continually, like that of our visible breath in frosty weather, or of the visible current of steam, or the smoking of a warm lake surface under sudden frost, be above that of the surrounding atmosphere; and yet I never remember entering a cloud without being chilled by it, and the darkness of the plague-wind, unless in electric states of the air, is always accompanied by deadly chill.

Nor, so far as I can read, has any proper account yet been given of the balance, in serene air, of the warm air under the cold, in which the warm air is at once compressed by weight, and expanded by heat, and the cold air is thinned by its elevation, yet contracted by its cold. There is indeed no possibility of embracing the conditions in a single sentence, any more than in a single thought. But the practical balance is effected in calm air, so that its lower strata have no tendency to rise, like the air in a fire balloon, nor its higher strata to fall, unless they congeal into rain or snow.

I believe it will be an extreme benefit to my younger readers if I write for them a little 'Grammar of Ice and Air,' collecting the known facts on all these matters, and I am much minded to put by my ecclesiastical history for a while, in order to relate what is legible of the history of the visible Heaven.