METEOROLOGY AND CLIMATE

Gulf Stream—Its beneficial influence—Meteorological tables— Mean temperatures, &c.—Arrangement of seasons—Range of temperature—Rainfall—Atmospheric moisture—Iodine, &c., in atmosphere — Winds — Botany corroborating results of Meteorology—Length of day, &c.—Aurora Borealis—Influence of Drainage on Climate.

A CASUAL observer, on finding Shetland was situated in 60° north, the same latitude as St Petersburg and of Cape Farewell in Greenland, would, in ignorance, conclude that its climate was as severe as that of the two last-mentioned places. Such an observer would be not a little surprised were he told the mean annual temperature of Shetland was not two degrees lower than that of Edinburgh. On learning that those islands are fully exposed to the genial influence of the Gulf Stream, and that the mean temperature of the sea on their coasts is upwards of 49° Fahrenheit, we have at once an explanation of the mildness of their climate. The Gulf Stream is so well known to impinge on the shores of Orkney and Shetland, as well as those of Great Britain and Ireland, that I need not enlarge on the fact, merely mentioning that besides giving them a high sea temperature, it also makes its presence known by carrying to their coasts the seeds of the Mimosa Scandens, and other West Indian productions. The beneficial influence of this famous oceanic current on the climate of Orkney is well stated by that well-known man of science, and excellent member of the medical and clerical professions, the Rev. Dr Clouston, minister of Sandwick, who says:—“The mean annual temperature of the sea is thus seen to be 3*19° above that of the air, while it is from 6° to 8° above it during January, February, October, November, and December, and decidedly below it only during May, June, and July, and even then less than lj° at an average.”1 One of the wise arrangements of Providence served by the Gulf Stream as regards Shetland is shown by Mr Buchan, Secretary of the Scottish Meteorological Society, who gives the normal winter temperature due at its latitude as 3°, but the actual temperature is 39°, thus indicating a gain of 36°.2 Another beneficial effect of the same current is to maintain the summer temperature at 53°, instead of the violent warmth of continental districts in the same latitude.

In attempting to make a few remarks on the climate of Shetland, I must acknowledge the kindness of the Rev. Dr Hamilton, minister of Bressay, who haB presented me with an elaborate meteorological document, containing the results of his observations for a period of sixteen years (1850-1865).

The following is the mean temperature for each month for sixteen years, deduced from said document:—

Taking from the above table the mean temperature for the seasons of the year as they are usually arranged, upwards of three months each, we have—

On glancing at this table, it is evident that to arrange the seasons here according to the usual method, at once leads us into absurdity; for what could be more absurd than to have the temperature of winter higher than that of spring, and that of autumn above that of summer? Can February and March, with temperatures of 38° and 38'87° respectively, be reckoned spring months, while the winter months of November and December have a temperature of 42*4° and 40*9° respectively? Even intelligent non-scientific observers acquainted with Shetland are aware that the months are not arranged in seasons there in the same way as in the rest of Britain.

For the islands under consideration, I would suggest the following arrangement of months in seasons as approximating to the truth :—

This arrangement is by no means absolutely correct, but it gives us the characteristic temperature of the seasons in something like the proper proportions, and pretty closely corresponds to the other meteorological phenomena which mark the different seasons. The chief objection to it at first sight is, that it makes the winter too long; but no person acquainted with Shetland can deny its winter is vety long. From unwillingness further to complicate the arrangement by splitting the months into fractions, I have classified November as belonging entirely to winter, but it appears to me its first half should be given to autumn, as it is generally marked by the prevalence of a “tract” of clear, calm, mild, comparatively warm weather, known in North America as the Indian summer, and called by the Shetlanders the “peerie simmer.” The mean annual temperature of Shetland, according to Dr Hamilton’s table, is 45*5°. Dr G. W. Spence, however, in his able thesis, calls it 46°, and as all mean annual temperatures that I have been able to find in meteorological works are expressed in “round numbers,” without fractions, let us call it 46°. The isothermal line of 46°, thus passing through Shetland in latitude 60°, would, according to the chart given in Dr Scoresby Jackson’s excellent work on medical climatology, descend to Copenhagen in latitude 55° on the one side, and to Fort Snelling in North America in latitude 44° on the other. Again, St Petersburg, the equal in latitude of Shetland, has the isothermal line of 40° passing through it—that same line which begins due north from these islands, and in latitude 70°. Bucharest, in Turkey, strange to say, presents the mean annual temperature of 46°.

Let us now contrast the temperature of Shetland for the whole year and its different months with a few places in Great Britain.

It appears that,.taking the winter temperature as 39°, and that of summer as 53°,2 we have in Shetland a range between these two seasons of only 14°, or between February (38°), the coldest, and August (54-43°), the hottest month, 16°. The coldest months in Edinburgh, Kendal, and Antrim are, respectively, December, 38*50°, January, 34*88°, and February, 32*00°; and the hottest months in the three places are July, 59*31°, August, 58*21°, and July, 60.75°; therefore their ranges of temperature are, in order, 20*61°, 23*33°, and 28*75°. Thus, taking Edinburgh, Kendal, and Antrim as specimens of districts in each of the three kingdoms, we have the range of temperature much less marked in Shetland than in them, and therefore may conclude that its climate, as far as the temperature of each month is concerned, is more equable than their climates.

The great defect in the Shetland climate, has, by all authors who have written on these islands, been said to be its extreme variability, but it is evident from the meteorological tables that the difference in temperature between the successive months is generally less in Shetland than elsewhere in the United Kingdoln, and that the mean difference between each month and those which follow it is also less there. Thus the transition in temperature is shown to be more gradual in Shetland than in the other districts. The monthly range of temperature in Shetland is less than that of Bute and Alderly, two British districts with which it may be compared, as regards every month in the year, except March and April. The daily range of temperature is only a fraction greater in Shetland than in Bute, usually reckoned the most mild climate in Scotland. These results gathered from the tables clearly show the temperature of these islands less variable than that of the other districts, which are not reckoned variable; and variability being purely a relative term, we may conclude that the climate of Shetland is not variable in temperature.

In such a district as Shetland, situated in the ocean, much intersected by arms of the sea, with large surfaces of evaporating fresh water, and the prevailing winds south-westerly, we would expect a large rainfall; but those conditions favourable to the deposition of atmospheric moisture in the form of rain are to a great extent counterbalanced by the mildness of the temperature and the absence of high hills. Thus as regards the rainfall, Shetland appears to occupy1 almost exactly an intermediate position between Edinburgh, which may be taken as a representative of an eastern, and Bute, a very good instance of a western, situation. The large rainfall at Kendal illustrates the effects of a western situation and propinquity to high hills. The larger rainfall in Orkney than in Shetland may be explained by the fact that in the former connty the observations were taken at Sandwick, a western, and in the latter at Bressay, an eastern, situation. Even granting the general rainfall of Shetland is as high as that of Orkney, it is then only “probably near the average of Scotland,” which conclusion is rather startling when we are often told that more rain falls in Shetland than in any part of Europe, and when we find places in Scotland which have from two to four times as much rain in the year as that remote county. “Thus, at Scathwaite, Borrowdale, the mean annual rainfall is 127 inches,” and “at a few places among the Moffat and Lead Hills the annual rainfall is occasionally 70 to 75 inches.” But it may be argued that, although there is not a great quantity of moisture precipitated in the form of rain, yet, remaining in the air, it renders it moist, and consequently produces a “damp” climate.

To get at the truth on this point we have only to look at barometrical phenomena. The following table8 exhibits the mean height of the barometer in Shetland, compared with two other places :—

From this table it appears the mean annual height of the barometer is exactly the same at Bressay, in Shetland, as at Sandwick, in Orkney. The effect of the western situation of Sandwick, and the eastern position of Bressay, appears to be counterbalanced from the observations being taken at the former station 94, and at the latter only 7 or 8, feet above the level of the sea. At both these places the height of the barometer is shown to be, for one year, only 0*12 inches below that of Worthing, a favourite watering-place on the south coast of England, with a mean annual temperature of 51*3°, and an annual rainfall of 29 *5 inches, and the climate of which is not damp. If comparison with such a place be of any value, the conclusion is not unwarrantable that the barometer does not indicate an excessive amount of moisture in the Shetland atmosphere. The readiness with which metallic substances tarnish appears to me explicable on the supposition of iodine, in some form or other, being suspended in small particles in the atmosphere. During, and after a low tide, when extensive beds of sea-weed are exposed to atmospheric influence, the characteristic smell of iodine is. distinctly perceptible, even a considerable distance from the shore. Chloride of sodium and other sea salts are, in greater or less quantities, suspended in the air, as is proved by their deposition on the window panes of houses in inland situations. All these substances entering the system through the lungs undoubtedly influence—probably beneficially—the health of the community.

The next important constituent of climate to be considered is the direction of the winds from Dr Scoresby Jackson’s “Medical Climatology,” p. 350. Worthing has been introduced from the great difficulty of finding barometrical phenomena in works on climate.

TABLE1

SHOWING THE DIRECTION OF THE WINDS FOR THE DAYS OF THE TEAR, TAKING THE MEAN OF THE TEARS 1856-57-58-59.

This table gives us a considerable preponderance of southerly and westerly winds over those coming from the north and east. In this respect, however, Shetland is behind Scotland as a whole, and its northern districts. Shetland, however, enjoys more of the benign influence of the south-west winds than the other districts. To this circumstance, together with the impaction of the Gulf Stream on its shores, its mild climate is mainly to be attributed. It is worthy of remark that the winds here seldom blow either directly from the east or west, but much more commonly from the north-east or south-west. From what has been said regarding the winter temperature of both air and sea, and the nature of the prevailing winds, it will be easily understood why frost and snow are not only rare in occurrence, but also show in continuance. Of this a very homely practical illustration may be given : Shetlanders seldom learn to skate, because it is only every third or fourth winter they have frost sufficiently severe to admit of that healthful exercise.

The tendency of all the foregoing remarks in this chapter is to show that, in temperature, in rainfall, in the direction of the winds, and in direct exposure to the influence of the Gulf Stream, the Shetlands have decidedly a “western" climate. Here botany corroborates the results of meteorology. The well-known plant, Jesione Montana, is exceedingly common in all parts of Shetland. It is almost unknown on the east-coast of Scotland, but occurs abundantly in the western districts. The very presence of the Jesione indicates a mild climate. As to seasons, the days are very long in summer, when Shetland is favoured with even a greater amount of light than is due to its latitude. This is owing partly to the atmosphere being such as to produce a great amount of refraction, and partly to the sea acting as a reflector. From the end of May to the beginning of July, night is absolutely unknown, and what should be midnight—the twilight, much resembling the noon-day light in the depth of winter—is sufficiently strong to admit of the smallest print being read with ease. A clergyman who visited Shetland in the summer time, .on his return to London preached a sermon on the subject, and with rather more profanity than wisdom, took for his text the words—“And there shall be no night there,” after which he went on to describe the permanence t of the day in summer, from the late setting and early rising of the sun, and in winter from the very brilliant^Aurora Borealis efficiently “officiating” for the “orb of day ” during his absence. But in winter the days are comparatively short. Dr Edmondston toys—“On the 22nd December, which is the shortest day in the year, the sun rises seventeen and a half minutes past nine o’clock, and sets forty-two minutes and a half past two o’clock. He is, therefore, five hours and twenty-five minutes above the horizon. But besides this, there is a considerable degree of light both before his rising and after his setting; and when the atmosphere is clear, the influence is protracted for several hours after his complete disappearance.” This last remark of Dr E.’s is very just, as twilight is very much prolonged, as well as the corresponding gradual appearance of light before the rising of the sun.

The Aurora Borealis often presents itself with great brilliancy during the winter nights. But it is as fitful in its periods of occurrence, as in its position in the sky when present. In some winters it occurs frequently, in others it is very seldom seen. Writing in 1808, Dr Edmondston remarks—“The Aurora Borealis . . . has not appeared in the atmosphere of Zetland for the last few years so frequently, nor with such splendour, as formerly.”  Thunder is by no means common, and it is also very irregular in its periods of appearance. The ordinary force of the wind is decidedly greater than throughout Great Britain; and storms are of common occurrence, particularly in winter. They are frequently sudden in their outset, and sometimes very severe. Having referred to them in Chapter I., I need not say more regarding them. To this very imperfect sketch, I may add that the climate of Shetland is likely to undergo a great improvement by agricultural progress, particularly by the formation of surface-drains through the hills, by which vast quantities of water, now removed by evaporation, will be carried to the streams, and ultimately^ to the sea. Not only does the great amount of evaporation naturally lower the temperature, but the stagnation of water in the soil both averts growth, and tends to create miasmata, injurious both to vegetable and to animal life. Mr Umphray, of Reawick, has told me that since the draining of a shallow, stagnant loch on his estate, the “mildew” from which used to blight the crops in autumn, the harvests have been reaped with perfect safety in the neighbourhood. No doubt the beneficial effect of this change on the health of the population surrounding the former swamps is correspondingly great.