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of Edinburgh, Session 1867 - 68 . 
the pressure. The lines of 30 inches and upwards were coloured 
red, and the lines representing pressures less than 30 inches were 
coloured blue. Thus, the portions of the earth’s surface where the 
pressure was above or below the average (30 inches) could be seen 
at once. 
Mean Atmospheric Pressure for July.— The lowest pressures occur 
over the land and the highest over the ocean ; or, the lowest 
pressures occur in the north hemisphere and the highest in the 
south hemisphere. The greatest extent of high pressure extends 
quite round the globe from a little south of the equator to 40° lat. 
south. In the South Atlantic, in lat. 20°, this rises to 30*348 
inches ; in the North Atlantic there is a corresponding area of high 
pressure rising at lat. 35° to full 30*348 inches; and this region of 
high pressure extends over the south-west of Europe and the south- 
east of the United States. There is also a region of high pressure 
in the North Pacific, but it only amounts to about 30*1 inches. 
The greatest extent of low pressure occurs in Asia, amounting in 
the central regions of the Continent only to 29*5 inches. Pressures 
are also low in the interior of North America, and round the north 
and the south poles. 
Mean Atmospheric Pressure for January .- — In January the highest 
pressures are over the land and the lowest over the ocean; or, the 
highest are in the north hemisphere and the lowest in the south 
hemisphere. Thus, taken in a general sense, the mean pressures 
of July and January are reversed. 
The region of highest pressure occurs in the interior of Asia, 
where it amounts to 30*4 inches, being thus nearly one inch greater 
in winter than in summer. The area of high barometer (above 30 
inches) is continued westward through Europe south of the North 
Sea and the Baltic; the north of Africa; the North Atlantic, be- 
tween 15° and 45° lat. ; North America, except the north and north- 
west; the West India Islands; and the North Pacific, as far west 
probably as 150° long. W. The effect of the Mediterranean and 
adjoining seas, which are at this season warmer than the land, in 
lowering the mean winter pressure, and thus breaking the con- 
tinuity of the isobarometric 30*2 inches, and preventing its exten- 
sion from the Pacific to the north of the Lena, in Siberia, is very 
striking. All the charts show similar disturbances of the lines of 
