48 



REPORT — 1859. 



period. It will be noticed that the annual fall increases with the altitude of the 

 station above the sea-level. 



Remarks on the Climate of Orkney. By the Rev. Charles Clouston, 

 L.R.C.S. Edinb., Pres. Ork. Nat. Hist. Soc. fyc. 



Orkney is situated further North than any part of the mainland of Scotland or the 

 Naze of Norway, and nearly in the same latitude as Stockholm on the East, and 

 Cape Farewell on the West ; yet its climate is one of the most equable in Britain, and 

 this is ascribed to the effect of the surrounding oceans, and particularly of the Gulf- 

 stream. 



From meteorological observations made in Orkney for nearly thirty-three years, 

 tables of which were laid before the Section, it has been ascertained that its mean 

 annual temperature is not only equal to that of the north and middle of Scotland, 

 but even to that of the south border, or46°-26; while Dumfriesshire is 4° or 5° colder 

 than Orkney in winter, it is above 3° warmer in summer. This arrangement may be 

 pleasant, or favourable to animal life, but it is unfavourable to vegetation, particularly 

 to trees. Evergreens are killed by the sea-spray in winter. The difference between 

 the mean temperature of the warmest and coldest months is only about 17°, never 

 having risen so high as 62°, nor fallen so low as 31°. 



That the Atlantic moderates the extremes and elevates the temperature of winter, 

 more than it depresses that of summer, is evident, when we consider that in 1858 its 

 mean temperature was about 3£° above that of the air, which it exceeded during ten 

 months, and only fell below it during June and August. It has not yet been found 

 colder than 43°, and the mean of three years is 49°"56, or more than 3° above that 

 of the air. 



In the inland parts of Britain the greatest heat occurs about the middle of July, and 

 the greatest cold about the middle of January ; and the months equidistant from 

 these are most nearly of equal temperature. In Orkney, however, January and 

 February are equally cold, and July and August equally* warm ; and the months 

 equidistant from these correspond most nearly, as March and December. 



This retardation of the period of extreme heat and cold is ascribed to the influence 

 of the sea, which is neither so quickly heated in summer, nor cooled in winter, as the 

 surface of the land. 



A table was produced showing the mean monthly atmospheric pressure for the 

 last twenty years, which does not show any great peculiarity of climate. It attains its 

 greatest height in May, and gradually descends on each side, the only exception being 

 in September, when it takes a step upwards. The mercury has been observed as low 

 as 27*69 inches, and as high as 3076 inches, giving a range during these twenty 

 years of 3-07 inches. 



A table showing the quantity of rain each month for the last eighteen years was also 

 produced, showing that the mean annual quantity for that time is 3653 inches at 

 the place of observation on the west side, but it is much less on the east side of the 

 islands. As in the former tables, so in this may be observed a gradation from the 

 minimum to the maximum quantity ; thus May has the least rain as well as the 

 highest barometer, and it gradually increases on each side till October, which is the 

 wettest month, September being the only exception. 



From a table giving the direction of the wind for thirtv-two years, it appears that it 

 blew from the W., S.W., S. and S.E., 6964 days, while from the opposite four points- it 



