E. Loomis— Observations of the U. S. Signal Service. 105 
circulated about Mobile. If all this precipitation is regarded 
onging to the storm No. 21, it makes a total of 17:60 
inches for that day. No. 15 presents another case in which 
the rain-fall in column 8th is made to appear very small in 
consequence of the rule above stated, but if all the rain in- 
cluded within the system of circulating winds for that day were 
counted, the total would be 12:19 inches. We see then that 
these cases of fast moving barometric minima were generally 
accompanied by a large rain-fall; but there are apparently some 
cases in which the rain-fall which can be associated with these 
low areas was very slight. Such were Nos. 2, 3 and 38. 
The area of rain generally extended a great distance in ad- 
vance of the storm center, the average distance being 667 miles, 
but there were several cases in which the rain extended but 
ed tw 
Systems of circulating winds, and was apparently levelled before 
the morning of September 3d. 
hat now is the cause of these rapid movements of storm 
centers? Several of them apparently resulted from the mutual 
influence of two low areas. In my 10th paper (this Journ., vol. 
Xvul, p. 5) I showed that on the Atlantic Ocean two low areas 
quently become merged in one. In such cases the eastern 
low area is generally retarded in its progress, and is sometimes 
turned backward toward the west. At the same time the 
Progress of the western low area must be accelerated. Such 
near our borders, although the geographical extent of the 
weather maps is too small to exhibit the full development of 
Jour, waren “asa: Vou, XIX, No. 110,—Fxs., 1880, 
