Meteorology Part 7

We know that without dust-particles there can be no fog, and that smoke supplies a vast amount of such particles. Therefore, in certain states of the atmosphere, the more smoke the more fog. In Mr. Evelyn's day the fog, which he called "presumptuous smoake," was at times so dense that men could hardly discern each other for the "clowd." His Majesty's only sister had complained of the damage done to her lungs by the contamination, and Mr. Evelyn was disgusted at the apathy of the people to do anything to remedy the nuisance. He deplored that that glorious and ancient city of London should wrap her stately head in "clowds of smoake, so full of stink and darknesse." He was of opinion that a method of charring coal so as to divest it of its smoke, while leaving it serviceable for many purposes, should be made the object of a very strict inquiry. And he was right. For it is now known that fog in a town is intensified by much smoke.

In a city like London or Glasgow, where a great river, fed by warm streams of water from gigantic works, pa.s.ses through its centre, fogs can never be entirely obliterated, for the dust-particles in the air (often four millions and upwards in the cubic inch) will seize with terrible avidity the warm vapour rising from the river. That is the main reason why fogs cannot there be put down. Smoke is being consumed to a great extent; yet we find particles of sulphur remaining, which seize the warm vapour and form fogs dense enough to check all traffic. The worst form of city fogs seems to be produced when the air, after first flowing slowly in one direction, then turns on its tracks and flows back over the city, bringing with it a black pall, the acc.u.mulated products of previous days, to which gets added the smoke and other impurities produced at the time.

What irritated Mr. Evelyn was that, outside of London, the air was clear when pa.s.sengers could not walk in safety within the city. So vexed was he about the contamination, that he made it the occasion of all the "cathars, phthisicks, coughs, and consumption in the city." He appealed to common sense to testify that those who repair to London soon take some serious illness. "I know a man," he said, "who came up to London and took a great cold, which he could never afterwards claw off again."

Mr. Evelyn proposed that, by an Act of Parliament, the nuisance be removed; enjoining that all breweries, dye-works, soap and salt boilers, lime-burners, and the like, be removed five or six miles distant from London below the river Thames. That would have materially helped his cause.

But there is more difficulty in the purification than he antic.i.p.ated. Yet there was pluck in the old man pointing out the killing contamination and suggesting a possible remedy. He had the fond idea that thereby a certain charm, "or innocent magick," would make a transformation scene like Arabia, which is therefore "styl'd the Happy, attracting all with its gums and precious spices." In purer air fogs would be less dense, breathing would be easier, business would be livelier, life would be happier.

Few, I suppose, have laid their hands on this curious Latin thesis, or its quaint translation, directing the King's attention to the fogs that were ruining London. Since that time the city has increased, from little more than a village, to be the dwelling-place of six millions of human beings, yet too little improvement has been made in the removal of this fog nuisance. King Edward's drive through London would be even more dangerous on a muggy, frosty day than was Charles II.'s, when science was little known.

CHAPTER XXV

ELECTRICAL DEPOSITION OF SMOKE

A good deal of scientific work is being done in the way of clearing away fog and smoke; and this, through time, may have some practical results in removing a great source of annoyance, illness, and danger in large towns.

Sir Oliver Lodge and Dr. Aitken have been throwing light upon the deposition of smoke in the air by means of electricity.

If an electric discharge be pa.s.sed through a jar containing the smoke from burnt magnesium wire, tobacco, brown paper, and other substances, the dust will be deposited so as to make the air clear. Brush discharge, or anything that electrifies the air itself, is the most expeditious.

If water be forced upwards through a vertical tube (with a nozzle one-twentieth of an inch in diameter), it will fall to the ground in a fine rain; but, if a piece of rubbed (electrified) sealing-wax be held a yard distant from the place where the jet breaks into drops, they at once fall in large spots as in a thunder-shower. If paper be put on the ground during the experiment, the sound of pattering will be observed to be quite different. If a kite be flown into a cloud, and made to give off electricity for some time, that cloud will begin to condense into rain.

Experiments with Lord Kelvin's recorder show that variations in the electrical state of the atmosphere precede a change of weather. Then, with a very large voltaic battery, a tremendous quant.i.ty of electricity could be poured into the atmosphere, and its electrical condition could be certainly disturbed. If this could be made practically available, how useful it would be to farmers when the crops were suffering from excessive drought! It might be more powerfully available than the imagined condensation of a cloud into rain by the reverberation caused by the firing of a range of cannon.

But what is the practical benefit of this information? If electricity deposits smoke, it might be made available in many ways. The fumes from chemical works might be condensed; and the air in large cities, otherwise polluted, might be purified and rendered innocuous. The smoke of chimneys in manufacturing works might be prevented from entering the atmosphere at all. In flour-mills and coal-mines the fine dust is dangerously explosive.

In lead, copper, and a.r.s.enic works, it is both poisonous and valuable.

Lead smelters labour under this difficulty of condensing the fume which escapes along with the smoke from red-lead smelting furnaces; and it was considered that an electrical process of condensation might be made serviceable for the purpose. At Bagillt, the method used for collecting or condensing the lead fume is a large flue two miles long; much is retained in this flue, but still a visible cloud of white-lead fume continually escapes from the top of the chimney. There is a difficulty in the way of depositing fumes in the flue by means of a sufficient discharge of electricity, viz. the violent draught which is liable to exist there, and which would mechanically blow away any deposited dust.

But Dr. Aitken suggests that regenerators might be used along with the electricity. The warm fumes might be taken to a cold depositor, where (by the ordinary law of cold surfaces attracting warm dust-particles) the impurities would be removed, and, when purified, the air would again be taken through a hot regenerator before being sent up the chimney. By a succession of these chambers, with the a.s.sistance of electric currents, the air, impregnated with the most deleterious particles, or valuable dust, could be rendered innocuous.

The sewage of our towns must be cleaned of its deleterious parts before being run into the streams which give drink to the lower animals, because an Act of Parliament enforces the process. Why, then, ought we not to have similar compulsion for making the smoke from chemical and other noxious works quite harmless before being thrown into the air which contains the oxygen necessary for the life of human beings?

There seems to be a good field before electricians to catch the smoke on the wing and deposit its dust on a large scale. This seems to be a matter beyond our reach at present, except in the scientist's laboratory; but certainly it is a "consummation devoutly to be wished."

CHAPTER XXVI

RADIATION FROM SNOW

One night a most interesting paper by Dr. Aitken, on "Radiation from Snow," was read by Professor Tait to the Fellows of the Royal Society of Edinburgh. I remember that Dr. Alex. Buchan--the greatest meteorologist living--spoke afterwards in the very highest terms of the subject-matter of the paper. This was corroborated by Lord Kelvin, Lord MacLaren, and Professor Chrystal.

Dr. Aitken had been testing the radiating powers of different substances.

Snow in the shade on a bright day at noon is 7 Fahr. colder than the air that floats upon it, whereas a black surface at the same is only 4 colder. This difference diminishes as the sun gets lower; and at night both radiate almost equally well.

I select, among the careful and numerous observations, the notes on January 19, 1886; for I took note of the cold of that day in my diary. It was the coldest day of the whole of that winter. The barometer was 288 inches, and the thermometer 4--that is, 28 of frost. According to Dr.

Buchan, that January had only two equal in average cold for fifty years.

On January 19, at 10 A.M., when the air was at 20 and the sky clear, a black surface registered 16 and the upper layer of snow 12, showing a difference of 4 when both surfaces were colder than the superinc.u.mbent air. It is curious to note that, on February 5 of the same year, at the same hour, when the sky was overcast, the air was at 23, the black surface registered 29, and the snow 25, showing again the difference of 4; but, in this case, both surfaces were warmer than the air. In both cases the radiation at night was equal.

This small absorbing power of snow for heat reflected and radiated from the sky during the day must have a most important effect on the temperature of the air. The temperature of lands when covered with snow must be much lower than when free from it. And, when once a country has become covered with snow, there will be a tendency towards glacial conditions.

But, besides being a bad absorber of heat from the sky, snow is also a very poor conductor of heat. On that very cold night (January 18), when there was a depth of 5-1/2 inches of snow on the ground, and the night clear, with strong radiation, the temperature of the surface of the snow was 3 Fahr., and a minimum thermometer on the snow showed that it had been down to zero some time before. A thermometer, plunged into the snow down to the gra.s.s, gave the most remarkable register of 32. Through the depth of 5-1/2 inches of snow there was a difference of temperature of 29. This was confirmed by removing the snow, and finding that the gra.s.s was unfrozen. As the ground was frozen when the snow fell, it would appear that the earth's heat slowly thawed it under the protection of the snow.

The protection afforded by the bad-conducting power of snow is of great importance in the economy of nature. How vegetation would suffer, were it exposed to a low temperature, unprotected by the snow-mantle! So that, though the continued snow cools the air for animals that can look after their own heating, it keeps warm the soil; and vegetation prospers under the genial covering. The fine rich look of the young wheat-blades, after a continued snow has melted, must strike the most careless observer. Instead of the half-blackened tips and semi-sickly blades, which we see in a field of young wheat after a considerable course of dry frost without snow, we have a rich, healthy green which shows the vital energy at work in the plants. Or even in the town gardens, after a continued snow has been melted away by a soft, western breeze, we are struck with the white, peeping buds of the snowdrop and the finely springing gra.s.s in the sward.

Yet the snow-covering gives durability to cold weather. This has been demonstrated by Dr. Woeikof, the distinguished Russian meteorologist. On this account the spring months of Russia and Siberia are intensely cold.

The plants, then, which in winter are unable by locomotion to keep themselves in health, are protected by the snow-mantle which chills the air for animals that can keep themselves in heat by exercise. What a grand compensating power is here!

CHAPTER XXVII

MOUNTAIN GIANTS

Some mysterious physical phenomena can be clearly explained by the aid of science. The mountain giants that at times haunt the lonely valleys, and strike with fear the superst.i.tious dwellers there, are only the enlarged shadows of living human beings cast upon a dense mist.

The two most startling of these "eerie" phenomena are the spectres of Adam's Peak and the Brocken.

The phenomena sometimes to be observed at Adam's Peak, in Ceylon, are very remarkable. Many travellers have given vivid accounts of these. On one occasion the Hon. Ralph Abercromby, in his praiseworthy enthusiasm for meteorological research, went there with two scientific friends to witness the strange appearance. The conical peak, a mile and a half high, overlooks a gorge west of it. When, then, the north-east monsoon blows the morning mist up the valley, light wreaths of condensed vapour pa.s.s to the right of the Peak, and catch the shadows at sunrise.

This party reached the summit early one morning in February. The foreglow began to brighten the under-surface of the stratus-cloud with orange, and patches of white mist filled the hollows. Soon the sun peeped through a c.h.i.n.k in the clouds, and they saw the pointed shadow of the Peak lying on the misty land. Then a prismatic circle, with the red inside, formed round the shadow. The meteorologist waved his arms about, and immediately he found giant shadowy arms moving in the centre of the rainbow.

Soon they saw a brighter and sharper shadow of the Peak, encircled by a double bow, and their own spectral arms more clearly visible. The shadow, the double bow, and the giant forms, combined to make this phenomenon the most marked in the whole world.

The question has been frequently asked: Why are such aerial effects not more widely observed? There are not many mountains of this height and of a conical shape; and still fewer can there be where a steady wind, for months together, blows up a valley so as to project the rising morning mist at a suitable height and distance on the western side, to catch the shadow of the peak at sunrise.

The most famous place in Europe for witnessing the awe-inspiring phenomenon is the Brocken, in Germany--3740 feet in height. The only great disappointment there is that the conditions rarely combine at sunrise or sunset to have "the spectre" successful.

In July 1892, my daughter and I were spending some weeks at Harzburg, and, of course, we had to visit the Brocken and take stock of the world-known phenomenon. At mid-day, the air at the flat summit was cold, clear, and hard. The boulders are of enormous size; and near the "Noah's Ark" Hotel and Observatory many are piled up in a ma.s.s, on which the observers stand at the appointed time for having their shadows projected on the misty air in the valleys.

At five o'clock in the afternoon the sky was brilliantly clear on the summit of the Brocken; but the wind was rising from the sun's direction, and the mist was filling up the wide-spread eastern valley. We stood on the "spectre" boulders, and our shadows were thrown on the gra.s.s, just as at home. However, they fell upon large patches of white heather, which there is very plentiful.

At six o'clock the sun was still shining beautifully, and we anxiously waited for the time when it would be low enough to raise our shadows to the misty wall. An hour afterwards, a hundred visitors were out, and many of us were on the "spectre" stones. There was great excitement in antic.i.p.ation of the weird appearances, which had attracted us from such a distance.

But, almost at the moment of success, the sun descended behind a belt of purple cloud, and all we saw was part of a rainbow on the misty hollow.

For the sun never appeared again. This was intensely saddening, seeing that, but for that stratum of cloud above the horizon, the phenomenon would have been graphically displayed.

The cold became suddenly intense, and we had to sleep with a freezing mist enveloping the hotel. In vain did we wait for the wakening call, to tell us of sunrise; for the sun could not pierce the mist, and we had to return home disappointed.