14. E. Loomis—Observations of the U. S. 8 Signal } Service. 
the United States, depression areas do not generally begin 
with extensivé precipitation, but the rain-fall is a con- 
comitant after the system of circulating winds has become 
pretty well established. The depression of the epee raee 
is the result of a system of circulating winds, and t 
most frequent cause producing such a system appears i: ve 
two or more areas of high pressure at a considerable distance 
quently 1,400 miles) from each other. Differences of — 
ature and of humidity are also important agents in producing 
and sustaining such a system of winds. When a system of 
circulating winds has been —* over a large extent of coun- 
try, there almost invariably results a fall of rain; and if the 
rain-fall is abundant, and pp over a nice are: s, it becomes 
a very important agent in modifying the direction and force of 
the winds. 
The principal question still remains undecided, why did the 
storms in table II pursue a course so nearly from south to 
atmosphere near the earth’s surface, and occasional departures 
of storm paths from this average track appear to be mainly 
due to causes which render the general movement of the 
atmosphere at such times different from the average movement. 
In table II it is seen that the average velocity of the winds on 
the south side of the storm’s center was somewhat greater than 
on the north side. This seems to indicate that at these times 
a wind from the south or southeast pressed towards the storm- 
area with unusual force. This wind extended to a height 
greater than 6,000 feet, as is shown by the observations on Mt. 
Washington whenever a storm center came into the neighbor- 
hood of that station. The following observations show the 
direction and force of the wind on that mountain during the 
progress of storm No. IV. Oct. 20.1, wind S.E. 75 5 miles ; 
Oct. 20.2, wind S.E. 78 miles; Oct. 20.3, wind S. E. 50 miles; 
Oct. 21.1, wind 8S. E. 55 miles ; Oct. 21.2, wind S.E. 38 miles. 
The observations also show that this south current extended to 
the height of the upper clouds. This is seen from Plate I, 
where the arrows indicate (not the direction of the surface 
winds), but the direction of the upper clouds, according to the 
2 ap of the Signal Service observations for Oct. 21.1, 1873. 
ese arrows conform in a remarkable degree to the direction 
of the surface winds, and seem to indicate that the system o: 
circulating winds which prevailed at the surface of the earth, 
extended to a height greater than 6,000 feet into the region of 
= Nps peu a C06 gd which is very uncertain and difficult 
important exception to the rule here 
