7 
E.. Loomis— Observations of the U. 8. Signal Service. 18 
Nearly all of these areas of high pressure were immediately 
followed by an area of low pressure on the west side. When 
the center of high pressure reached the middle of the continent, 
an area of low pressure was almost invariably indicated by the 
observations near the Pacific coast. As long as the center of 
Nos. 2,3 and 5. In No. 2, an area of high barometer, which 
advanced eastward very slowly, was immediately succeeded by 
another area of high barometer, and no considerable low was 
formed between them within the limits of the United States, 
but a low was apparently formed in Canada. In like manner, 
No, 3 was immediately succeeded by another area of hig 
barometer, and no considerable low was formed between them. 
n No. 5 a low area was apparently in process of formation on 
the west side, when another area of high pressure pushed in 
from the north and filled up the low area. Thus we see that 
an area of unusually high pressure is almost invariably suc- 
ceeded by an area of low pressure on its western side, at a dis- 
tance of about 1,200 miles, but occasionally a new area of high 
pressure pushes on immediately after the first, and prevents the 
formation of any considerable area of low pressure. 
Areas of unusually high pressure are thus seen to be gener- 
ally accompanied by areas of low pressure both on the east and 
west sides, and at an average distance of about 1,200 miles. 
Sometimes an area of high pressure is broad enough to cover 
the entire continent from ocean t as in November 17, 
o ocean, 
mode January 24, 1874, February 1 and 2, 1874, and February 
