Meteorology Part 10

cannot be touched by extremes of temperature; but ordinary mortals are mere puppets in the hands of the G.o.ddess 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 to the 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. Aurorae, 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 and pressure 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 much longer, 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.

CHAPTER x.x.xIV

THE "CHALLENGER" WEATHER REPORTS

The _Challenger_ Expedition, commenced by Sir Wyville Thomson, and after his death continued by Sir John Murray, with an able staff of a.s.sistants 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 the _Challenger's_ Weather 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, pa.s.sing 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 the _Challenger_ Report 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 ma.s.s 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 ma.s.s 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 the _Challenger_ Expedition, 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 4 A.M. and highest at 2 P.M. The relative humidity is just the reverse. When the temperature is highest, the saturation of the air is lowest, and _vice versa_. 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, h.o.a.r-frost.

The _Challenger_ Reports, 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 4 A.M., and highest from 2 to 4 P.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 the _Challenger_ observations that on the open sea the greatest number of thunder-storms occur from 10 P.M. to 8 A.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.

CHAPTER x.x.xV

WEATHER-FORECASTING

To foretell with any degree of certainty the state of the weather for twenty-four hours is of immense advantage to business men, tourists, fishermen, and many others. The weather is everybody's business. And the probabilities of accurate forecasts are so improving that all are more or less giving attention to the morning meteorological reports.

Weather-forecasting depends on the principle from vast experience that, if one event happens, a second is likely to follow. According to the extent and accuracy of the data, will be the strength of the probability of correct forecasts. And the great end of popular meteorology is to demonstrate this.

We have given some explanations of the weather in some respects unique; and a careful consideration of these explanations will the more convince the reader of the importance of the subject. No doubt the changes of the weather are extremely complex, at times baffling; and the wonder is that forecasts come so near the truth.

For instance, the year 1903 almost defied the ordinary rules of weather, for it broke the record for rainfall. And, last year, so repulsive and unseasonable was the spring, that there seemed to be a virtual "withdrawal" of the season. I wrote on it as "The Recession of Spring."

Speak about Borrowing Days! We had the equinoctial gales of March about the middle of April. On very few days had we "clear shining to cheer us after rain," for the bitter cold dried up any genial moisture. An old farmer remarked that "We're gaun ower faur North." No one could account for the backwardness of the season. Unless for the cheering songs of the grove-charmers, one would have forgotten the time of the year.

In March of this year, at Strathmore, the barometer fell from 305 inches (the highest for years) to 2865 in five days without unfavourable weather following. It again rose to 3005, then fell to 2845, followed by a rise to 287 without any peculiar change. But in two days it fell to 284 (the lowest for years), followed by a deluge of rain and a perfect hurricane for several hours, while the temperature was fortunately mild. It was only evident at the end that this universal storm had been "brewing" some days before.

All are familiar with the ordinary prognostics of good and bad weather. A "broch" round the moon, in her troubled heaven, indicates a storm of rain or wind. When the dark crimson sun in the evening throws a brilliant bronzed light on the gables and dead leaves, we are sure that there is an intense radiation from the earth to form dew, or even h.o.a.r-frost.

According to the meteorological folk-lore, the weather of the summer season is indicated by the foliation of the oak and ash trees. If the oak comes first into leaf, the summer will be hot and dry, if the ash has the precedence it will be wet and cold. Looking over the observations of the budding of these two trees for half a century, I find that the weather-lore adage has been pretty correct. The ash was out before the oak a full month in the years 1816, '17, '21, '23, '28, '29, '30, '38, '40, '45, '50, and '59; and the summer and autumn in these years were unfavourable. Again, the oak was out before the ash several weeks in the years 1818, '19, '20, '22, '24, '25, '26, '27, '33, '34, '35, '36, '37, '42, '46, '54, '68, and '69; the summers during these years were dry and warm, and the harvests were abundant. One can never think of this weather prognostic from nature without recalling the Swallow Song of Tennyson's "Princess":--

"Why lingereth she to clothe her heart with love, Delaying, as the tender ash delays To clothe herself, when all the woods are green?"

On a muggy morning a sudden clearness in the south "drowns the ploughman."

And yet enough blue in the sky "tae mak' a pair o' breeks" cheers one with the a.s.surance of coming dry and sunny weather. The low flying of the swallows betokens rain, as well as any unseasonable dancing of midges in the evening. Sore corns on the feet, and rheumatism in the joints, are direful precursors. The leaves are all a-tremble before the approach of thunder. But throughout this volume I have given many ill.u.s.trations.

But one of the largest and most important practical problems of meteorology is to ascertain the course which storms follow, and the causes by which that course is determined, so that a forecast may thereby be made, not only of the certain approach of a storm, but the particular direction and force of the storm. The method of conducting this large inquiry most effectively was devised by the French astronomer, Le Verrier--the great aspirant, with our own Couch Adams, for the discovery of the planet Neptune. He began to carry this out in 1858 by the daily publication of weather data, followed by a synchronous weather map, which showed graphically for the morning of the day of publication the atmospheric pressure and the direction and force of the wind, together with tables of temperature, rainfall, cloud, and sea disturbances from a large number of places in all parts of Europe. It is from similar maps that forecasts of storms are still framed, and suitable warnings issued; and a ma.s.s of information is being collected by telegraph from sixty stations in the British Islands, &c., of the state of the weather at eight o'clock every morning, and a.n.a.lysed and arranged at the Meteorological Office in London for the evening's forecasts over the different districts of the country. A juster knowledge is being now acquired of those great atmospheric movements, and other changes, which form the groundwork of weather-forecasting.

The Meteorological Office, Westminster (entirely distinct from the Royal Meteorological Society), is administered by a Council (Chairman, Sir R.

Strachey; Scottish member, Dr. Buchan), selected by the Royal Society. It employs a staff of over forty. The chief departments relate to: (1) Ocean Meteorology, including the collection, tabulation, and discussion of meteorological data from British ships, the preparation of ocean weather charts, and the issue of meteorological instruments to the Royal Navy and Mercantile Marine; (2) Weather Telegraphy, including the reception of telegrams thrice a day from selected stations for the preparation of the daily reports and weather forecasts. Representatives of newspapers, &c., receive copies of the 11 A.M. forecast based on the 8 A.M. observations; and also of the 8.30 P.M. forecasts based on the observations received earlier in the day. In summer and autumn harvest forecasts are issued by telegraph to individuals who will defray the cost. The Office also collects climatological data from a number of voluntary and some subsidised stations. The "first order" stations include Valentia, Falmouth, Kew, and Aberdeen. These have self-recording instruments of high precision, giving a continuous record of the meteorological elements.

A Government Commission which sat last year, under the Rt. Hon. Sir Herbert Maxwell, Bart., have issued a Report, recommending a number of changes in the management and const.i.tution of the Meteorological Office; and considerable modifications are not unlikely to take place in the near future. In his evidence before that Commission, the Chairman of the Council acknowledged that the great function of meteorologists is the collection of facts; but the interpretation of those collected facts, in a scientific manner, is still in a very immature condition. Dr. Buchan, in his evidence, confessed that forecasting by the Council is purely "by rule of thumb." It is not possible to lay down hard and fast rules for forecasting.

With regard to the storm-warning telegrams, as a rule, the earliest trustworthy indication of the approach of a dangerous storm to the coasts of the British Isles precedes the storm by only a few hours. Delays are therefore very serious.

It is admitted by the best British meteorologists that the observations of the United States are better conducted, although the best instruments in the world are set and registered at Kew, in England. The work of weather forecasts and storm warnings is carried on with the highest degree of prompt.i.tude and efficiency at the Washington Central Office. This is because the work of predictions has been hitherto the chief work of the Office: the entire time of the observers, on whose telegraphic reports the forecasts are based, is controlled by the United States Weather Bureau; and the right of precedence in the use of wires is maintained.

Professor Bruckner, of Berne, has devoted a lifetime to the comparatively new treatment of climatic oscillations, based upon observations made at 321 points on the earth's surface, distributed as follows: Europe, 198; Asia, 39; N. America, 50; Cen. and S. America, 16; Australia, 12; Africa, 6. One of his conclusions is that an average time of about thirty-five years is found to intervene between one period of excess or deficiency of warmth and the next, accompanied by the opposite relative condition of moisture.

All are familiar with the hoisting of cone-warning as indication of a coming storm. This work is exceedingly important, especially for those connected with the sea by business or pleasure. On the known approach of a cyclone of dangerous intensity, special messages are sent from the London Meteorological Office, warning the coasts likely to be affected. When the cone is hoisted with its apex downwards, it means that strong south or south-west winds are to be looked for. When the cone is hoisted with its apex upwards, it indicates that strong winds from the north or north-east are expected. Of course they are merely useful precautions; but they are universally attended to by people on the sea-coast.

Though one may have reasonable doubts about the use that can be made of weather forecasts for three days, such as are now regularly issued, on account of the finical, coy, spasmodic interludes on short notice, yet there is a wonderful certainty in the daily prognostics of the direction and strength of the wind, the temperature of the air, and the likelihood of rainy or fair weather, dependent on the broad uniformity of nature.

This is very serviceable for people who have now to live at high pressure in business, in the enthralling days of keen compet.i.tion. And it is a great boon to those who are in search of health by travelling, or who, in innocent pleasure, desire to live as much as possible in the open air.

Very little credit is given to the "gas" of the isolated "weather prophet"; but those who have confidence in the usual weather forecasts from the Meteorological Office are satisfied in their belief; and those who, in self-confidence, ignore all weather prognostics, are still weak enough to read them and act up to them.

In practical meteorology, in the scientific explanation of popular weather-lore, and in the study of atmospheric phenomena, which so powerfully influence us, for gladness or discomfort, we may, as with other branches of science, even all our days, cheerfully go on in "the noiseless tenor of our way,"

"Nourishing a youth sublime, With the fairy tales of science and the long results of time."