A SANITARY DETECTIVE
The impure state of the air in the rooms of a house can now be determined by means of colour alone. Dr. Aitken has invented a very simple instrument for that purpose; and this ought to be of great service to sanitary officers. It is called the koniscope—or dust-detective.
The instrument consists of an air-pump and a metal tube with glass ends. Near one end of the test-tube is a passage by which it communicates with the air-pump, and near the other end is attached a stop-cock for admitting the air to be tested. It is not nearly so accurate as the dust-counter; but it is cheaper, more easily wrought, and more handy for quick work. All the grades of blue, from what is scarcely visible to deep, dark blue, may be attached alongside the tube on pieces of coloured glass; and opposite these colours are the numbers of dust-particles in the cubic inch of the similar air, as determined by the dust-counter.
While the number of particles was counted by means of the dust-counter, the depth of blue given by the koniscope was noted; and the piece of glass of that exact depth of blue attached. A metal tube was fitted up vertically in the room, in such a way that it could be raised to any desired height into the impure air near the ceiling, so that supplies of air of different degrees of impurity might be obtained. Toproduce the impurity, the gas was lit and kept burning during the experiments. The air was drawn down through the pipe by means of the air-pump of the koniscope, and it passed through the measuring apparatus of the dust-counter on its way to the koniscope. It may be remarked that, by a stroke of the air-pump, the air within the test-tube is rarefied and the dust-particles seize the moisture in the super-saturated air to form fog-particles; through this fog the colour is observed, and the shade of colour determines the number of dust-particles in the air. These colours are named “just visible,” “very pale blue,” “pale blue,” “fine blue,” “deep blue,” and “very deep blue.”
When making a sanitary inspection, the pure air should be examined first, and the colour corresponding to that should be considered as the normal health colour. Any increase from the depth would indicate that the air was being gradually contaminated; and the amount of increase in the depth of colour would indicate the amount of increase of pollution.
As an illustration of what this instrument can detect, a room of 24 by 17 by 13 feet was selected. The air was examined before the gas was lighted, and the colour in the test-tube was very faint, indicating a clear atmosphere. In all parts of the room this was found the same. A small tube was attached to the test-tube, open at the other end, for taking air from different parts of the room. Three jets of gas were then lit in the centre of the room, and observations at once begun with the koniscope.
Within thirty-five seconds of striking the match tolight the gas, the products of combustion had extended near the ceiling to the end of the room; this was indicated by the colour in the koniscope suddenly becoming a deep blue. In four minutes the deep-blue-producing air was got at a distance of two feet from the ceiling. In ten minutes there was strong evidence of the pollution all through the room. In half-an-hour the impurity at nine feet from the floor was very great, the colour being an intensely deep blue.
The wide range of the indications of the instrument, from pure clearness to nearly black blue, makes the estimate of the impurity very easily taken with it; and, as there are few parts to get out of order, it is hoped it may come into general use for sanitary work.
FOG AND SMOKE
Just two hundred and forty years ago, Mr. John Evelyn, F.R.S., a well-known writer on meteorology, sent a curious tract to King Charles II., which was ordered to be printed by his Majesty. It was entitled “Fumifugium,” and dealt with the great smoke nuisance in London. I find from the thesis that he had a very hazy idea of the connection between fog and smoke; and no wonder, for it is only lately that the connection has been fully explained.
We know that without dust-particles there canbe 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, passes 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 flowsback over the city, bringing with it a black pall, the accumulated 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 passengers 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 anticipated. 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 ruiningLondon. 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.
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 passed 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 theexperiment, 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 quantity 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 arsenic 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 condensingthe 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 assistance 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.”
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 28·8 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 10A.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 superincumbent air. It is curious to note that, on February 5of 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 5½ 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 grass, gave the most remarkable register of 32°. Through the depth of 5½ inches of snow there was a difference of temperature of 29°. This was confirmed by removing the snow, and finding that the grass 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 itexposed 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 grass in the sward.
Yet the snow-covering gives durability to cold weather. This has been demonstrated by Dr. Wœikof, 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!
MOUNTAIN GIANTS
Some mysterious physical phenomena can be clearly explained by the aid of science. The mountaingiants that at times haunt the lonely valleys, and strike with fear the superstitious 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 pass 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 chink 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 aërial 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 mass, 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 grass, 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 anticipation 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.
Sometimes the rainbow colours assume the shapes of crosses instead of circles. Occasionally a bright halo will be seen above the shadow-head of the observer, concentric rainbows enclosing all. In some recorded cases the grand effect must have been simply glorious.
Scientific observation has done much to dispel the superstition which has clung so tenaciously to the Highland mind. The lonely grandeur of the weird mountain giants has been clearly explained as perfectly natural, yet the awe-striking feeling cannot be entirely driven off.
THE WIND
Once was the remark pointedly made: “The wind bloweth where it listeth.” And that is nearly true still. The leading winds are under the calculation of the meteorologist, but the others will not be bound by laws.
Yet there are instruments for measuring the velocity and force of the wind, after it is on; but “whence it comes” is a different matter. A gentle air moves at the rate of 7 miles an hour; a hurricane from 80 to 150 miles, pressing with 50 lbs. on the square foot exposed to its fury. Some of the gusts of the Tay Bridge storm, in 1879, had a velocity of 150 miles an hour, with a pressure of 80 to 90 lbs. to the square foot.
Before steamers supplanted so many sailing vessels, seamen required to be always on the alert as to the direction and strength of the wind, and the likelihood of any sudden change; and they chronicled twelve different strengths from “faint air” to a “storm.”
In general, the wind may be considered to be the result of a change of pressure and temperature in the atmosphere at the same level. The air of a warmer region, being lighter, ascends, and gives place to a current of wind from a colder region. These two currents—the higher and the lower—will continue to blow until there is equilibrium.
The trade winds are regular and constant. Thesewere much followed in the days of old. A vast amount of air in the tropics gets heated and ascends, being lighter, and travels to the colder north. A strong current rushes in from the north to take its place. But the earth rotates round its axis from west to east, and the combined motions make two slant wind directions, which are called the “trade winds,” because they were so important in trade navigation.
Among the periodical winds are the “land and sea breezes.” During the day, the land on the sea coast is warmer than the sea; accordingly, the air over the land becomes heated and ascends, the fine cool breeze from the sea taking its place. Towards evening there is the equilibrium of temperature which produces a temporary calm. Soon the earth chills, and the sea is counterbalancingly warm—as sea-water is steadier as to temperature than is land—the air over the sea becomes warmer, and ascends, the current from the land rushing in to take its place. Hence during the night the wind is reversed, until in the morning again the equilibrium is restored and there is a calm, so far as these are concerned. These are therefore called the “land and sea breezes.” Of course, it is within the tropics that these breezes are most marked. By the assistance of other winds, a hurricane will there occasionally destroy towns and bring about much damage and loss of life; but better that hundreds should perish by a hurricane than thousands by the pestilence which, but for the storm, would have done its dire work.
In countries where the differences of pressure are more marked than the differences of temperature,in the surrounding regions the strength of the wind thereby occasioned is far stronger than the land and sea breezes.
The variable winds are more conflicting. These depend on purely local causes for a time, such as “the nature of the ground, covered with vegetation or bare; the physical configuration of the surface, level or mountainous; the vicinity of the sea or lakes, and the passage of storms.” Among these winds are the simoom and sirocco.
Theeastwinds, which one does not care about in the British Islands during the spring time, are occasioned by the powerful northern current which rushes south from the northern regions in Europe. Dr. Buchan points out a very common mistake among even intelligent observers who shudder at the hard east winds. It is generally held that these winds are damp. They are unhealthy, but they are dry. It is quite true that many easterly winds are peculiarly moist; all that precede storms are so far damp and rainy; and it is owing to this circumstance that, on the east coast of Scotland, the east winds are searching and carry most of the annual rainfall there. But all of these moist easterly winds, however, soon turn to some westerly point. The real east wind, so much feared by invalids, does not turn to the west; it is exceeding dry. Curious is it that brain diseases, as well as consumption, reach their height in Britain while east winds prevail. Once in Edinburgh, during the early spring, I had rheumatic fever, and during my convalescence my medical adviser, Dr. Menzies, would not let me have a short drive until the wind changed to the west. The first thing Ianxiously watched in the morning was the flag on the Castle; and for nearly two months it always waved from the east. How heart-depressing!
Creatures are we in the hands of nature’s messengers. We so much depend upon the weather for our happiness. Joyful are we when the honey-laden zephyr waves the long grass in June, or when
“The gentle wind, a sweet and passionate wooer,Kisses the blushing leaf.”
Compared with this, how terrible is Shakespeare’s allusion to the appalling aspects of the storm:—
“I have seen tempests, when the scolding windsHave rived the knotty oaks; and I have seenThe ambitious ocean swell, and rage and foam,To be exalted with the threat’ning clouds;But never till to-night, never till now,Did I go through a tempest dropping fire.”
CYCLONES AND ANTI-CYCLONES
The criticism of the weather in the meteorological column of our daily newspapers invariably speaks of “cyclones.” It is, therefore, advisable to give as plain an explanation of these as possible. Cyclones are “storm-winds.” Their nature has to be carefully studied by meteorologists, who are industriously at work to ascertain some scientific basis for the atmospheric movements.
What is the cause of the spiral movement instorm-winds? In their centre the depression of the barometer is lowest, because the atmosphere there is lightest. As the walls of the spiral are approached, the barometer rises.
Dr. Aitken has ingeniously hit upon an experiment to illustrate a spiral in air. All that is necessary is a good fire, a free-going chimney, and a wet cloth. The cloth is hung up in front of the fire, and pretty near it, so that steam rises readily from its surface; and, when there are no air-currents in the room, the steam will rise vertically, keeping close to the cloth. But if the room has a window in the wall, at right angles to the fireplace, so as to cause the air coming from it to make a cross-current past the fire, then a cyclone will be formed, and the vapour from the cloth will be seen circling round. When the cyclone is well formed, all the vapour is collected into the centre of the cyclone, and forms a white pillar extending from the cloth to the chimney. This experiment shows that no cyclone can form without some tangential motion in the air entering the area of low-pressure.
Now to illustrate the spiral approach. Fill with water a cylindrical glass vessel, say 15 inches in diameter and 6 inches deep. Have an orifice with a plug a little from the centre of the bottom. Remove the plug, the water runs out, passing round the vessel in a vortex form. But, as the passage between the orifice (or centre of the cyclone) and the temporary division is narrower than in any other place, the water has to pass this part much more quickly than at any other place. And this curious result is observed: the top of the cyclone no longer remainsover the orifice, buttravelsin the direction of the water which is moving most speedily. Similar to this is the cyclone in the atmosphere; its centre also moves in the direction of the quickest flowing wind that enters it.
Dr. Aitken is of opinion that, in forecasting storms, too little attention has been paid to theanti-cyclones. They do more than simply follow and fill up the depression made by the cyclones. They initiate and keep up their own circulation, and collect the materials with which the cyclones produce their effect. Neither could work efficiently without the other.
Suppose a large area on the earth over which the air is still in bright sunshine. After a time, when the air gets heated and charged with vapour, columns of air would begin to ascend in a disorderly fashion. But suppose an anti-cyclone is blowing at one side of this area. When the upper air descends to the earth, it spreads outwards in all directions; but the earth’s rotation interferes and changes the radial into a spiral motion. The anti-cyclonic winds will prevent the formation of local cyclones, and drive all the moist, hot air to its circumference, just above the earth. The anti-cyclone forces its air tangentially into the cyclone, and gives it its direction and velocity of rotation, also the direction and rate of travel of the centre of depression. The earth’s rotation is the original source of the rotatory movements, but both intensify the initial motion.
Accordingly, the cyclone must travel in the direction of the strongest winds blowing into it, just as the vortex in the vessel with the eccentric orificetravelled in the direction of the quickest moving water. This is verified by a study of the synoptic charts of the Meteorological Office.
The sun’s heat has always been looked upon as the main source of the energy of our winds, but some account must also be taken of the effects of cold. It is well known that the mean pressure over Continental areas is high during winter and low during summer. As the sun’s rays during summer give rise to the cyclonic conditions, so the cooling of the earth during winter gives rise to anti-cyclonic conditions. It is found during the winter months in several parts of the Continent that as the temperature falls the pressure rises, producing anti-cyclones over the cold area; whereas, when the temperature begins to rise, the pressure falls, and cyclones are attracted to the warming area.
Small natural cyclones are often seen on dusty roads, the whirling column having a core of dusty air, and the centre of the vortex travelling along the road, tossing up the dust in a very disagreeable way to pedestrians. Sometimes such a cyclone will toss up dry leaves to a height of four or five feet. They are very common; but it is only when dust, leaves, or other light material is present that they are visible to the eye.
RAIN PHENOMENA
The soft rain on a genial evening, or the heavy thunder-showers on a broiling day, are too well knownto be written about. Sometimes rain is earnestly wished for, at other times it is dreaded, according to the season, seed-time or harvest. Some years, like 1826, are very deficient in rainfall, when the corn is stunted and everything is being burnt up; other years, like 1903, there is an over-supply, causing great damage to agriculture. The year 1903 will long be remembered for its continuous rainfall; it is the record year; no year comes near it for the total rainfall all over the kingdom.
Rain is caused by anything that lowers the temperature of the air below the dew-point, but especially by winds. When a wind has blown over a considerable area of ocean on to the land, there is a likelihood of rain. When this wind is carried on to higher latitudes, or colder parts, there is a certainty of rain. Of course, in the latter case the rain will fall heavier on the wind side than on the lee side.
For short periods, the heaviest falls or “plouts” of rain are during thunder-storms. When the raindrops fall through a broad, cold stratum of air, they are frozen into hail, the particles of which sometimes reach a large size, like stones. Of course, water-spouts now and again are of terrible violence.
One of the heaviest rainfalls yet recorded in Great Britain was about 2¼ inches in forty minutes at Lednathie, Forfarshire, in 1887. Now 1 inch deep of rain means 100 tons on an imperial acre; so the amount of water falling on a field during that short time is simply startling. The heaviest fall for one day was at Ben Nevis Observatory, being fully 7¼ inches in 1890. In other parts of the world this is far exceeded. In one day at Brownsville, Texas,nearly 13 inches fell in 1886. On the Khasi hills, India, 30 inches on each of five successive days were registered. At Gibraltar, 33 inches were recorded in twenty-six hours.
The heaviest rainfalls of the globe are occasioned by the winds that have swept over the most extensive ocean-areas in the tropics. On the summer winds the rainfall of India mainly depends; when this fails, there is most distressing drought. Reservoirs are being erected to meet emergencies.
From Dr. Buchan’s statistics it is found that the annual rainfall at Mahabaleshwar is 263 inches; at Sandoway 214; and at Cherra-pungi 472 inches, the largest known rainfall anywhere on the globe. Over a large part of the Highlands of Scotland more than 80 inches fall annually, while in some of the best agricultural districts there it does not exceed 30 inches.
Of all meteorological phenomena, rainfall is the most variable and uncertain. Symons gives as tentative results from twenty years’ observations in London—(1) In winter, the nights are wetter than the days; (2) in spring and autumn, there is not much difference; (3) in summer, nearly half as much again by day as by night.
The wearisomeness of statistics may be here relieved by a short consideration of thesplashof a drop of rain. Watching the drop-splashes on a rainy day in the outskirts of the city, when unable to get out, I brought to my recollection the marvellous series of experiments made by Professor A. M. Worthington in connection with these phenomena. Of course, I could not see to proper advantage the formation ofthe splashes, as the heavy raindrops fell into these tiny lakes on the quiet road. There is not the effect of the huge thunder-drops in a stream or pool. The building up of the bubbles is not here perfect, for the domes fail to close, nor are the emergent columns visible to the naked eye. It is a pity; for R. L. Stevenson once wrote of them in his delightful “Inland Voyage,” when he canoed in the Belgian canals, as thrown up by the rain into “an infinity of little crystal fountains.”
Beautiful is this effect if one is under shelter, every dome seeming quite different in contour and individuality from all the rest. But terrible is it when out fishing on Loch Earn, even with the good-humoured old Admiral, when the heavy thunder-drops splash up the crystal water, and one gets soaked to the skin, sportsman-like despising an umbrella.
There is, however, a scientific interest about the splash of a drop. The phenomenon can be best seen indoors by letting a drop of ink fall upon the surface of pure water in a tumbler, which stands on white paper. It is an exquisitely regulated phenomenon, which very ideally illustrates some of the fundamental properties of fluids.
When a drop of milk is let fall upon water coloured with aniline dye, the centre column of the splash is nearly cylindrical, and breaks up into drops before or during its subsequent descent into the liquid. As it disappears below the surface, the outward and downward flow causes a hollow to be again formed, up the sides of which a ring of milk is carried; while the remainder descends to be torn a second time into a beautiful vortex ring. Thisshell or dome is a characteristic of all splashes made by large drops falling from a considerable height, and is extremely pretty. Sometimes the dome closes permanently over the imprisoned air, and forms a large bubble floating upon the water. The most successful experiments, however, have been carried through by means of instantaneous photography, with the aid of a Leyden-jar spark, whose duration was less than the ten-millionth of a second. But the simple experiments, without the use of the apparatus, will while away a few hours on a rainy afternoon, when condemned to the penance of keeping within doors.
THE METEOROLOGY OF BEN NEVIS
Several large and very important volumes of the Royal Society of Edinburgh are devoted to statistics connected with the meteorology of Ben Nevis. Most of the abstracts have been arranged by Dr. Buchan; while Messrs. Buchanan, Omond, and Rankine have taken a fair share of the work.
This Observatory, as Mr. Buchanan remarks, is unique, for it is established in the clouds; and the observations made in it furnish a record of the meteorology of the clouds. It is 4406 feet above the level of the sea; and as there is a corresponding Observatory at Fort William, at the base of the mountain, it is peculiarly well fitted for important observations and weather forecasting. Themountain, too, is on the west sea-coast of Scotland, exposed immediately to the winds from the Atlantic, catching them at first hand. It is lamentable to think that, when the importance of the observations made at the two Observatories was becoming world known, funds could not be got to carry them on. Ben Nevis is the highest mountain in the British Islands, best fitted for meteorological observations; yet these have been stopped for want of money.
Dr. Buchan’s valuable papers were published before any one dreamed of the stoppage of the work, which had such an important bearing on men engaged in business or taken up with open-air sport. From these I shall sift out a few facts that even “mute, inglorious” meteorologists may be interested in knowing.
For a considerable time the importance of the study of the changes of the weather has come gradually to be recognised, and an additional impetus was given to the prosecution of this branch of meteorology when it was seen that the subject had intimate relations to the practical question of weather forecasts, including storm warnings. Weather maps, showing the state of the weather over an extensive part of the surface of the globe, began to be constructed; but these were only indicators from places at the level of the sea.
The singular advantages of a high-level observatory occurred to Mr. Milne Home in 1877; and Ben Nevis was considered to be in every respect the most suitable in this country. The Meteorological Council of the Royal Society of London offered in 1880, unsolicited, £100 annually to the ScottishMeteorological Society, to aid in the support of an Observatory, the only stipulation being that the Council be supplied with copies of the observations.
From June to October, in 1881, Mr. Wragge made daily observations at the top of the Ben; and simultaneous observations were made, by Mrs. Wragge, at Fort William. A second series, on a much more extended scale, was made in the following summer.
Funds were secured to build an Observatory; and, in November 1883, the regular work commenced, consisting of hourly observations by night as well as by day. Until a short time ago, these were carried on uninterruptedly. Telegraphic communications of each day’s observations were sent to the morning newspapers; and now we are disappointed at not seeing them for comparison.
The whole of the observations of temperature and humidity were of necessity eye-observations. For self-registering thermometers were comparatively useless when the wind was sometimes blowing at the rate of 100 miles an hour. Saturation was so complete in the atmosphere that everything exposed to it was dripping wet. Every object exposed to the outside frosts of winter soon became thickly incrusted with ice. Snowdrifts blocked up exposed instruments. Accordingly, the observers had to use their own eyes, often at great risks.
The instruments in the Ben Nevis Observatory, and in the Observing Station at Fort William, were of the best description. Both stations were in positions where the effects of solar and terrestrial radiation were minimised. No other pair of meteorological stations anywhere in the world are so favourablysituated as these two stations, for supplying the necessary observations for investigating the vertical changes of the atmosphere. It is to be earnestly hoped, therefore, that funds will be secured to resume the valuable work.
The rate of the decrease of temperature with height there is 1° Fahr. for every 275 feet of ascent, on the mean of the year. The rate is most rapid in April and May, when it is 1° for each 247 feet; and least rapid in November and December, when it is 1° for 307 feet. This rate agrees closely with the results of the most carefully conducted balloon ascents. The departures from the normal differences of temperature, but more especially the inversions of temperature, and the extraordinarily rapid rates of diminution with height, are intimately connected with the cyclones and anti-cyclones of North-Western Europe; and form data, as valuable as they are unique, in forecasting storms.
The most striking feature of the climate of Ben Nevis is the repeated occurrence of excessive droughts. For instance, in the summer and early autumn of 1885, low humidities and dew-points frequently occurred. Corresponding notes were observed at sea-level. During nights when temperature falls through the effects of terrestrial radiation, those parts of the country suffer most from frosts over which very dry states of the air pass or rest; whereas, those districts, over which a more humid atmosphere hangs, will escape. On the night of August 31 of that year, the potato crop on Speyside was totally destroyed by the frost; whereas at Dalnaspidal, in thedistrict immediately adjoining, potatoes were scarcely—if at all—blackened.
The mean annual pressure at Ben Nevis was 25·3 inches, and at Fort William 29·8, the difference being 4½ inches for the 4400 feet.
For the whole year, the difference between the mean coldest hour, 5A.M., and the warmest hour, 2P.M., is 2°. For the five months, from October to February, the mean daily range of temperature varied only from O·6 to 1·5. This is the time of the year when storms are most frequent; and this small range in the diurnal march of the temperature is an important feature in the climatology of Ben Nevis; for it presents, in nearly their simple form, the great changes of temperature accompanying storms and other weather changes, which it is so essential to know in forecasting weather.
The daily maximum velocity of the wind occurs during the night, the daily differences being greatest in summer and least in winter. A blazing sun in the summer daily pours its rays on the atmosphere, and a thick envelope of cloud has apparently but little influence on the effect of the sun’s rays. Thunder-storms are essentially autumn and winter phenomena, being rare in summer.
According to Mr. Buchanan, the weather on Ben Nevis is characterised by great prevalence of fog or mist. In continuously clear weather it practically never rains on the mountain at all. In continuously foggy weather, on the other hand, the average daily rainfall is 1 inch. There is a large and continuous excess of pressure in clear weather over that of foggy weather. The mean temperature of the year is3½ degrees higher in clear than in foggy weather. In June the excess is 10 degrees. The nocturnal heating in the winter is very clearly observed. This has been noticed before in balloons as well as on mountains. The fog and mist in winter are much denser than in summer. Whether wet or dry, the fog which characterises the climate of the mountain is nothing butcloudunder another name.
THE WEATHER AND INFLUENZA
Some remarkable facts have been deduced by the late Dr. L. Gillespie, Medical Registrar, from the records of the Royal Infirmary of Edinburgh. He considered that it might lead to interesting results if the admissions into the medical wards were contrasted with the varying states of the atmosphere. The repeated attacks of influenza made him pay particular attention to the influence of the weather on that disease.
The meteorological facts taken comprise the weekly type of weather,i.e.cyclonic or anti-cyclonic, the extremes of temperature for the district for each week, and the mean weekly rainfall for the same district. More use is made of the extremes than of the mean, for rapid changes of temperature have a greater influence on disease than the actual mean.
The period which he took up comprises the seven years 1888-1895. There was a yearly average of admissions of 3938; so that he had a good field forobservation. Six distinct epidemics of influenza, varying in intensity, occurred during that period; yet there had been only twenty-three attacks between 1510 and 1890. Accordingly, these six epidemics must have had a great influence on the incidence of disease in the same period, knowing the vigorous action of the poison on the respiratory, the circulatory, and the nervous systems. The epidemics of influenza recorded in this country have usually occurred during the winter months.
The first epidemic, which began on the 15th of December 1889 and continued for nine weeks, was preceded by six weeks of cyclonic weather, which was not, however, accompanied by a heavy rainfall. Throughout the course of the disease, the type continued to be almost exclusively cyclonic, with a heavy rainfall, a high temperature, and a great deficiency of sunshine. The four weeks immediately following were also chiefly cyclonic, but with a smaller rainfall.
The summer epidemic of 1891 followed a fine winter and spring, during which anti-cyclonic conditions were largely prevalent. But the epidemic was immediately preceded by wet weather and a low barometer. It took place in dry weather, and was followed by wet, cyclonic weather in turn.
The great winter epidemic of 1891 followed an extremely wet and broken autumn. Simultaneously with the establishment of an anti-cyclone, with east wind, practically no rain, and a lowering temperature, the influenza commenced. Great extremes in the temperature followed, the advent of warmer weatherand more equable days witnessing the disappearance of the disease.
The fourth epidemic was preceded by a wet period, ushered in by dry weather, accompanied by great heat; and its close occurred in slightly wetter weather, but under anti-cyclonic conditions. The fifth outbreak began after a short anti-cyclone had become established over our islands, continued during a long spell of cyclonic weather with a considerable rainfall, but was drowned out by heavy rains. The last appearance of the modern plague, of which Dr. Gillespie’s paper treats, commenced after cold and wet weather, continued in very cold but drier weather, and subsided in warmth with a moderate rainfall.
The conditions of these six epidemics were very variable in some respects, and regular in others. The most constant condition was the decreased rainfall at the time, when the disease was becoming epidemic. Anti-cyclonic weather prevailed at the time.
According to Dr. Gillespie, the tables seem to suggest that a type of weather, which is liable to cause catarrhs and other affections of the respiratory tract, precedes the attacks of influenza; but that the occurrence of influenza inepidemic formdoes not appear to take place until another and drier type has been established. As the weather changes, the affected patients increase with a rush.
He is of opinion that the supposed rapid spread of influenza on the establishment of anti-cyclonic conditions may be explained in this way. The air in the cyclonic vortex, drawn chiefly from the atmosphere over the ocean, is moist, and contains none ofthe contagion; the air of the anti-cyclone, derived from the higher strata, and thus from distant cyclones, descending, blows gently over the land to the nearest cyclone, and, being drier, is more able to carry suspended particles with it. He considers that temperature has nothing to do with the problem, except in so far as the different types of weather may modify it. The Infirmary records point to the occurrence of similar phenomena, recorded on previous occasions. Accordingly, if such meteorological conditions are not indispensable to the spread of influenza in epidemic form, they at least afford favourable facilities for it.
CLIMATE
One is not far up in years, in Scotland at any rate, without practically realising what climate means. He may not be able to put it in words, but easterly haars, chilling rimes, drizzling mists, dagging fogs, and soddening rains speak eloquently to him of the meaning of climate.
Climate is an expression for the conditions of a district with regard to temperature, and its influence on the health of animals and plants. The sun is the great source of heat, and when its rays are nearly perpendicular—as at the Tropics—the heat is greater on the earth than when the slanted rays are gradually cooled in their passage. As one passes to a higher level, he feels the air colder, until hereaches the fluctuating snow-line that marks perpetual snow.
The temperature of the atmosphere also depends upon the radiation from the earth. Heat is quite differently radiated from a long stretch of sand, a dense forest, and a wide breadth of water. Strange is it that a newly ploughed field absorbs and radiates more heat than an open lea. The equable temperature of the sea-water has an influence on coast towns. The Gulf Stream, from the Gulf of Mexico, heats the ocean on to the west coast of Britain, and mellows the climate there.
The rainfall of a district has a telling effect on the climate. Boggy land produces a deleterious climate, if not malaria. Over the world, generally, the prevailing winds are grand regulators of the climate in the distinctive districts. A wooded valley—like the greatest in Britain, Strathmore—has a health-invigorating power: what a calamity it is, then, that so many extensive woods, destroyed by the awful hurricane twelve years ago, are not replanted!
Some people can stand with impunity any climate; their “leather lungs” cannot be touched by extremes of temperature; but ordinary mortals are mere puppets in the hands of the goddess climate. Hence health-resorts are munificently got up, and splendidly patronised by people of means. The poor, fortunately, have been successful in the struggle for existence, by innate hardiness, otherwise they would have had a bad chance without ready cash for purchasing health.
It may look ludicrous at first sight, but it seems none the less true, that the variation of the spots on the sun have something to do with climate, even tothe produce of the fields. On close examination, with a proper instrument, the disc of the sun is found to be here and there studded with dark spots. These vary in size and position day after day. They always make their first appearance on the same side of the sun, they travel across it in about fourteen days, and then they disappear on the other side. There is a great difference in the number of spots visible from time to time; indeed, there is what is called the minimum period, when none are seen for weeks together, and a maximum period, when more are seen than at any other time. The interval between two maximum periods of sun-spots is about eleven years. This is a very important fact, which has wonderful coincidences in the varied economy of nature.
Kirchhoff has shown, by means of the spectroscope, that the temperature of a sun-spot must be lower than that of the remainder of the solar surface. As we must get less heat from the sun when it is covered with spots than when there are none, it may be considered a variable star, with a period of eleven years. Balfour Stewart and Lockyer have shown that this period is in some way connected with the action of the planets on the photosphere. As we have already mentioned, the variations of the magnetic needle have a period of the same length, its greatest variations occurring when there are most sun-spots. Auroræ, and the currents of electricity which traverse the earth’s surface, follow the same law. This remarkable coincidence set men a-thinking. Can the varying condition of the sun exert any influences upon terrestrial affairs? Is it connected with the variation of rainfall, the temperature andpressure of the atmosphere, and the frequency of storms? Has the regular periodicity of eleven years in the sun-spots no effect upon climate and agricultural produce?
Mr. F. Chambers, of Bombay, has taken great trouble to strike, as far as possible, a connection between the recurring eleven years of sun-spots and the variation of grain prices. He arranged the years from 1783 to 1882 in nine groups of eleven years; and, from an examination of his tables, we find that there is a decided tendency for high prices to recur at more or less regular intervals of about eleven years, and a similar tendency for low prices. An occasional slight difference can be accounted for by some abnormal cause, as war or famine.
Amid all the apparently irregular fluctuations of the yearly prices, there is in every one of the ten provinces of India a periodical rise and fall of prices once every eleven years, corresponding to the regular variation which takes place in the number of sun-spots during the same period. If it were possible to obtain statistics to show the actual out-turn of the crops each year, the eleven yearly variations calculated therefrom might reasonably correspond with the sun-spot variations even more closely than do the price variations.
This is a remarkable coincidence, if nothing more. What if it were yet possible to predict the variations of prices in the coming sun-spot cycle? Such a power would be of immense service. By its aid it could be predicted that, as the present period of low prices has followed the last maximum of sun-spots, which was in the year 1904, it will not last muchlonger, but that prices must gradually keep rising for the next five years. Could science really predict this, it would be studied by many and blessed by more. Yet the strange coincidence of a century’s observations renders the conclusions not only possible, but to some extent probable.
THE “CHALLENGER” WEATHER REPORTS
TheChallengerExpedition, commenced by Sir Wyville Thomson, and after his death continued by Sir John Murray, with an able staff of assistants for the several departments, was one of the splendid exceptions to the ordinary British Government stinginess in the furtherance of science. The results of the Expedition were printed in a great number of very handsome volumes at the expense of the Government.
And the valuable deductions from theChallenger’sWeather Reports by Dr. Alex. Buchan, in his “Atmospheric Circulation,” have thrown considerable light upon oceanic weather phenomena. For some of his matured opinions on these, I am here much indebted to him.
Humboldt, in 1817, published a treatise on “Isothermal Lines,” which initiated a fresh line for the study of atmospheric phenomena. An isotherm is an imaginary line on the earth’s surface, passing through places having a corresponding temperature either throughout the year or at any particular period. An isobar is an imaginary line on the earth’s surface,connecting places at which the mean height of the barometer at sea-level is the same. To isobars, as well as to isotherms, Dr. Buchan has devoted considerable attention. In 1868, he published an important series of charts containing these, with arrows for prevailing winds over the earth for the months of the year. In this way what are called synoptic charts were established.
In theChallengerReport are shown the various movements of the atmosphere, with their corresponding causes. It is thus observed that the prevailing winds are produced by the inequality of the mass of air at different places. The air flows from a region of higher to a region of lower pressure,i.e.from where there is an excessive mass of air to fill up some deficiency. And this is the great principle on which the science of meteorology rests, not only as to winds, but as to weather changes.
Of the sun’s rays which reach the earth, those that fall on the land are absorbed by the surface layer of about 4 feet in thickness. But those that fall on the surface of the ocean penetrate, as shown by the observations of theChallengerExpedition, to a depth of about 500 feet. Hence, in deep waters the temperature of the surface is only partially heated by the direct rays of the sun. In mid-ocean the temperature of the surface scarcely differs 1° Fahr. during the whole day, while the daily variation of the surface layer of land is sometimes 50°. The temperature of the air over the ocean is about three times greater than that of the surface of the open sea over which it lies; but, near land, this increases to five times.
The elastic force of vapour is seen in its simplest form on the open sea, as disclosed by these Reports. It is lowest at 4A.M.and highest at 2P.M.The relative humidity is just the reverse. When the temperature is highest, the saturation of the air is lowest, andvice versâ. So on land when the air, by radiation of heat from the earth, is cooled below the dew-point, dew is produced, and, at the freezing-point, hoar-frost.
TheChallengerReports, too, show that the force of the winds on the open sea is subject to no distinct and uniform daily variation, but that on nearing land the force of the wind gives a curve as distinctly marked as the ordinary curve of temperature. That force is lowest from 2 to 4A.M., and highest from 2 to 4P.M.Each of the five great oceans gives the same result. At Ben Nevis, on the other hand, these forces are just reversed in strength.
It is also shown by theChallengerobservations that on the open sea the greatest number of thunder-storms occur from 10P.M.to 8A.M.And, from this, Dr. Buchan concludes that over the ocean terrestrial radiation is more powerful than solar radiation in causing those vertical disturbances in the equilibrium of the atmosphere which give rise to the thunder-storm.