6 E.. Loomis— Observations of the U. S. Signal Service. 
Storm No. 12 was quite peculiar, having aaa a path 
almost directly opposite to that of ordinary storms. During 
the afternoon of Aug. 20th, 1878, there was an area of low 
pressure (29°75) over West Virginia, being part of a greater 
depression whose center was over New cardiac and there 
was a slight sides to the formation of an in dependent sys- 
tem of circulating winds. Owing to a slight increase of pres- 
sure on the north side, this low area was crowded southward, 
and in the afternoon of Aug. 21st assumed the character of an 
independent low area ae ff 8) with a feeble system of circulat- 
ing winds. At 7.35 A. M. Aug. 22d, this low center had been 
crowded south to lat. 30°, ‘the greatest observed depression 
appears to illustrate the general character of areas of low pres- 
sure, and shows that their progressive movement is not due to 
a simple drifting of the atmosphere, but rather to a diminution 
of pressure on one side of the low area and an increase of pres- 
sure on the other side. In the present case, there was scarcely 
any appreciable diminution of pressure on the south side, and 
only a slight increase of pressure on the north side. 
oe 
American storms advancing Northerly and Easterly. 
The storms which cross the United States north of the par- 
allel of 88 degrees, generally pursue a course a little to the 
north of east; while those which come from the region south 
of lat. 38 degrees generally pursue a course nearly northeast, 
especially in the neighborhood of the Atlantic coast. During 
the summer months few storm-centers travel south of the par- 
allel of 88°, and davies this period the average course of 
storms is almost exactly towards the east. 
The following table shows those cases in which storms have 
traveled northward and eastward, and came from a point as far 
south as lat. 26°. The arrangement of the table is similar to 
that of the preceding. Columns 3 and 4 show the position of 
the storm-center at the beginning and end of the northeasterly 
motion, as far as is indicated by the observations; column 7t 
shows the lowest pressure reported, and column 8th gives a 
brief indication of the previous course of the storm. On Plate 
II these tracks are oo and are designated by the same 
numbers as in the ta 
We see from this table that storms of this class occur most 
frequently in the autumn, and least frequently in summer. 
One of these storms began near lat. 15°; two began near lat. 
20°; and seventeen of them began south of lat. 24°, 
