TIMPOLHESLS OF CAUSE OF GLACIAL PERIODS Th 
the general features of atmospheric pressure and circulation. 
An inspection of Buchan’s isobaric maps shows that there are, 
north of 45° north latitude, two nearly permanent areas of low 
barometer and one of f#zgh barometer. (See accompanying 
sketch maps I and 2, based mainly on Buchan’s.) The area of 
high barometer is located in Asia on the meridian of 100° east 
longitude. It may perhaps be regarded as one of the normal 
high areas that theoretically belong to the parallel of 30° north 
latitude, but which has been displaced 20° to the northward by the 
topographic conditions of the great Eurasian continent. Its two 
chief companions under this view lie, the one in the east Atlantic 
centering near the Azores, about 30° north latitude and 25° west 
longitude, the other in the east Pacific, off the coast of Califor- 
nia, in about 35° north latitude and 140° west longitude. But 
the Asiatic area of high pressure seems to combine in itself also 
the function of a polar center, for no other center, high or low, 
lies between it and the pole. Moreover, it is above mid-lati- 
tude, and is nearer the parallels of the two permanent areas 
of low pressure of the arctic region than to those of its 30° cor- 
relatives, for it lies itself in 50° north latitude, while the arctic 
“lows” lie in 55° and 60° north latitude respectively. 
Furthermore, as shown on Buchan’s map 52, these high-lati- 
tude centers are arranged about the pole at nearly equal distances 
from each other, the’ Asiatic ‘high’ being: in about 100° east 
longitude, the north Atlantic ‘‘low” in about 35° west longitude, 
and the north Pacific ‘‘low”’ in about 170° west longitude, z. ¢., 
their successive distances from each other. are.135°, 145°, and 
140°. While these centers shift somewhat during the seasons, 
they are essentially fixed, the above statements being based on 
the isobaric averages for the year. These centers are therefore 
to be distinguished from the familiar moving cyclonic centers 
and are to be regarded as enduring factors which express the 
essentially permanent circulatory features of the circumpolar 
atmosphere. The Asiatic ‘‘high” is a permanent anti-cylonic 
area characterized by descending outward-flowing currents, 
attended by low precipitation and clear air. The north Atlantic 
