260 EF. Loomis— Contributions to Meteorology. 
If we enquire for the cause of the low temperature which 
generally attends areas of high pressure, I think we must admit 
that the low temperature is in part the cause and in part the 
effect of the high pressure. A low temperature increases the 
density of the air, and the height of a given weight of air is 
thereby diminished. Its pressure is not however thereby 
increased, but the void left in the upper regions of the atmos- 
phere must be filled by air flowing in from neighboring regions, 
and the pressure over the cold area is thus increased. The 
reduced temperature becomes indirectly a cause of increased 
pressure. This high pressure accompanied by extreme cold 
generally results in a calmand dry atmosphere free from clouds. 
The heat of the earth’s surface is now rapidly dissipated by radia- 
tion, and thus the high pressure becomes a source of increased 
cold. High pressureand low temperature reénforce each other, 
and they are almost invariably associated, particularly in the 
extremely high pressures which occur during the colder months 
of the year. 
The long duration of areas of high pressure over Huropasia 
appears to be due to the favorable conditions for the formation 
of such areas which prevail in this part of the world during the 
winter months. During this period, areas of low pressure of 
extreme violence prevail almost uninterruptedly over the 
Atlantic Ocean, and the air which here ascends moves eastward 
and settles down over Huropasia. This is a vast continent, the 
central portions of which are removed to a great distance from 
any large body of water. Here the sources of atmospheric dis- 
turbances are few—the air is generally tranquil and without 
much cloudiness—the heat of the earth is rapidly wasted by 
radiation—and the low temperature reénforces the high pres- 
sure. Thus during the winter months, high pressure over Asia 
becomes as habitual as low pressure over the Atlantic Ocean. 
During each of the winters from 1878 to 1884 the areas of 
high pressure over Europasia exhibited characteristics similar 
to those we have found for the winter of 1877-8. In the win- 
ter of 1878-9 from Dec. 18, 1878 to Feb. 11, 1879, a period of 
56 days, an area of high pressure prevailed over a large portion 
of Kuropasia, and during this period the pressure at the center 
at po time sunk below 30°5 inches. At three different times 
during this period the barometer rose above 31:0 inches and it 
attained a maximum of 31:26 inches. During the winter of 
1879-80 an area of high pressure prevailed over Huropasia 
from Jan. 5th to March 4th, 1880, a period of 60 days without 
at any time sinking below 30°5 inches; and on eight different 
days the pressure was as high as 31:0 inches, the maximum 
being 31°17 inches. During the winter of 1881-2 an area of 
high pressure prevailed over some part of Huropasia from Nov. 
