g(52 WINDS OF THE GLOBE. 



Buchaii lias rendered a great service to meteorology by extending Buys-Ballot's 

 law to the general phenomena of the winds of the globe. He collected a great 

 deal of information as to the mean pressure of the air, and drew isobaric Imes, 

 i. c, lines of equal pressure of the air reduced to sea-level, and by considering 

 the prevailing winds he proved that they generally followed Buys-Ballot's law. 

 As this work, " Mean Pressure and Prevailing Winds of the Globe," is very 

 important in the discussion of the winds, I make the following extracts from it: — 



" Distribution of Atmospheric Pressure in December, January, and February. 



"In these months the highest pressures are grouped over the land of the 

 Northern Hemisphere, and the larger the extent of land, the greater the pressure. 

 The area of high barometer (thirty inches and upwards) embraces nearly all of 

 Asia, all Europe south of the North and Baltic Seas, the North Atlantic between 

 15°-45° N., the West Indies, North America except the North and Northwest, 

 and the Northern Pacific between 8° and 24° N. There are also two regions of 

 high pressure of comparatively small extent, the one in the South Atlantic, the 

 other in the South Pacific. 



"The regions of low pressure are: the northern part of the North Atlantic and 

 North Pacific, including portions of the continent adjoining; the belt of low 

 pressure in the equatorial region, towards which the trade-winds blow, and the 

 remarkable depression in the Antarctic region which is probably subject to little 

 change throughout the year. 



" In March the pressure diminishes over Asia, the middle and south of Europe 

 and the United States. Everywhere else except in the tropics it is rising. This 

 rise of pressure is most apparent in the temperate regions of the southern hemi- 

 sphere. In the north of the Atlantic it is rapidly rising, the average pressure in 

 Iceland now being 29.609 inches, thus showing an increase of 0.34 inch in com- 

 parison with January. 



" In April, the heavy lines indicating a pressure above the average have all but 

 left Asia, Europe, and the United States, and the isobars of 30 inches bound a belt 

 of high pressure, which completely encircles the globe in the south temperate 

 zone. Pressure continues to rise in the north of the Atlantic, and to the north of 

 North America. And it is probable that a space of high pressure (at least 30 

 inches) completely encircles the north pole. In this month pressure is more 

 equally distributed than in any other month ; for, except the Antarctic Ocean, it 

 scarcely rises anywhere above 30.1 inches nor falls below 29.8. In May, in North 

 Europe, in Greenland, and in the north of North America, pressure attains the 

 maximum of the year. Pressure continues to increase in the south temperate 

 zone, and the isobar of 30.1 now nearly encircles the globe. At this time the 

 highest pressure in the southern hemisphere occurs in the S. E. of Australia, 

 where, at Deniliquin, it is 30.185 inches. Pressure is rapidly falling over Asia and 

 the United States. 



"In June, July and August, pressure falls in the central regions of Asia to about 

 29.5. In this season this diminution of pressure, which may be regarded as entirely 



