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Meteorology; or Weather Explained

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<h2>CHAPTER XXXI</h2> 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. The mountain, 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 Scottish Meteorological 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 favourably situated 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 the district 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, 5 A.M., and the warmest hour, 2 P.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 is 3½ 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 but cloud under another name.     <hr style="width: 50%;" /> <div style="break-after:column;"></div>

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