THE BRITISH ISLES. 199 



the surrounding regions. At the centre of a Cyclonic area the level may 

 be above 30 inches, and it may be below 29-5 inches at the centre of an 

 Anti-Cyclonic system. 



Of these two classes, the latter is of rarer occurrence ; and whereas 

 the Cyclonic Storms travel with some rapidity, Anti-Cyclonic areas travel 

 much more slowly. It is a remarkable fact worth mentioning, that in 

 some places the Anti-Cyclonic areas are noticed to remain as it were sta- 

 tionary ; this is frequently the case at the entrance of the English Channel, 

 especially in early autumn, when they have been known to remain for 

 days together in the same locality. The centres of the Storms generally 

 pass on the Northern side of the British Isles, hence we get more of the 

 S.W., "West, and N.W. winds than of those Easterly winds which would 

 be found on the Northern side of the central area of lowest pressure. To 

 this fact we may attribute the prevalence of Westerly winds, shown in the 

 Table, drawn up from observations made at Liverpool. Owing to the 

 smallness of the area covered by the British Isles, it is seldom that a 

 perfect rotatory gale can be traced in its passage, but inferences are drawn 

 from the observations made on small portions of such Storms, at stations 

 in these islands and on the Continent. 



The best idea which we can gain, for practical purposes, of the winds 

 which affect us in these islands, is that the air over the Atlantic Ocean, 

 North of latitude 40° N., is constantly flowing from West to East, like a 

 gigantic river. If such a river be flowing rapidly, we often see on its 

 surface small waves, each with its own eddies and circulations, which are 

 carried on with the stream. If we Could look at the upper surface of the 

 atmosphere, we should see much the same sort of conditions, except that 

 what corresponds to the hollow of the wave would be a patch of defective 

 pressure, while that which corresponds to the crest of the wave would be 

 an area of excessive pressure. 



(129.) The more characteristic Winds of the West of Europe, and 

 especially of our own islands, are due to atmospheric disturbances pro- 

 ducing areas of high or low pressure ; the rapidity and intensity of the 

 development of which, with the direction of their paths and their position, 

 determine the force of the Wind, the direction in which it blows, and the 

 manner in which it veers or backs, that is, changes its direction. But 

 how the changes of pressure are determined, and what causes the transfer of 

 the disturbed area (commonly under the form of an atmospheric eddy or 

 vortex, in a definite direction, usually from West to East), is still to be 

 ascertained ; though here, too, it is obvious that the distribution of the 

 land and sea areas, and of the ocean currents, on which the temperature 

 of the superincumbent air so immediately depends, combined with the 

 rotatory motion of the earth, are among the principal agencies at work. 

 The winds of our islands have commonly, more or less distinctly, the 

 gyratory character, which is one of the secondary results of the rotation 

 of the earth.* 



* See "Lectures on Geography," delivered before the University of Cambridge, by 

 General R. Strachey, R.E., F. U.S., published in the Proceedings of the Royal Geogm- 

 pl.ioal Society, April, 1888, page 230. 



