416 ME. r. W. HAEMEE OK THE [Aug. I90I.. 



than the ocean during the summer, and therefore cyclonic; they 

 are colder in the winter and are then an ticy clonic, and, as in the 

 Southern Hemisphere, the anticyclones tend to leave the land for 

 the ocean as spring advances, and to return to it in autumn. The 

 high-pressure systems move also northward and southward with 

 the sun. Certain meteorological features are, however, more or less 

 permanent in the Northern Hemisphere. Anticyclones, forming a 

 portion of the northern belt of high pressure, exist near the Tropic 

 of Cancer, in the IN^orth Atlantic and in the North Pacific, at all 

 seasons (figs. 4 & 5, pp. 414 & 415), though their form and position 

 vary, not only from day to day, but seasonally also, and in winter 

 they are statistically confluent with the anticyclones of the adjacent 

 land-tracts. Well-marked areas of low pressure in the Northern 

 Hemisphere are, moreover, predominant over the oceans for a great 

 part of the year; one, shown in fig. 4, lies statistically in January 

 over the North Pacific, immediately to the south of Behring, 

 Strait. This tends to become smaller as summer approaches, and 

 nearly disappears during July (fig. 5), in the chart for which it 

 appears as a small protruding lobe of the great Asiatic cyclone. 



Low-pressure conditions largely prevail also in winter over the 

 North Atlantic, though the actual position and form of this, as^ 

 of other cyclonic systems, are constantly changing ; and in summer 

 it nearly disappears, being encroached upon by the Atlantic anti- 

 cyclone. 



The glaciated region of Greenland is always more or less an area 

 of higher pressure than that occupied by the low-pressure system^ 

 called, for convenience, the Icelandic cyclone, and the former 

 country is seldom traversed by the cyclonic disturbances which cross- 

 the Atlantic. They usually avoid it, passing well to the south. 



In the Northern as in the Southern Hemisphere the general 

 direction of the winds remains the same where the relative positions- 

 of high and low-pressure areas are unchanged, as in the case of the 

 north-easterly trades, which conform at all times of the year to 

 the more or less permanent relation between the anticyclone of the^ 

 Azores and the Equatorial belt of low pressure. Even in that part of 

 the Atlantic which lies north of lat. 40° N., and in the continents 

 adjoining (regions — during a great part of the year — of constant 

 atmospheric disturbance), although the isobaric lines are changing- 

 in direction and position from day to day, certain main features 

 predominate at different seasons. Dr. Buchan's monthly charts are 

 statistical only, and do not represent the actual conditions at any one 

 time, being based on the averages for a number of years. Still they 

 indicate generally the seasonal changes in the atmospheric conditions, 

 and in the prevalent direction of the winds, upon which the varying- 

 climate of the temperate regions of the Northern Hemisphere so largely 

 depends. It will be seen from these charts that it is to the position and 

 form of the Icelandic depression, and the predominance of southerly 

 and westerly winds over the British Isles and the Norwegian coast, even 



