Observations of the United States Signal Service. 19 
Direction. | Velocity. | Direction, | Velocity. 
Fort Sully _..| N.W. 36 miles. ||Davenport_.._| 8.W. 18 miles. 
Datauth 222. N.E. ane Leavenworth Ss. LB 
Chicago ____- Ss. Ee Escanaba_._--| 8.E. PE ae 
Grand Haven S. 19 “  ||Omaha--.-.- Ss. 162" 
The distribution of the cases of small rain-fall mentioned in 
the table on pages 14 and 15, according to the seasons of the 
year, is as follows: 
Spring, 14 cases. Summer, 4 cases. 
Autumn, 39 and 21 cases. Winter, 23 cases. 
We see that these cases occur most frequently in the autumn 
and especially in the month of October. They are generally 
accompanied by a hazy or smoky condition of the atmosphere, 
and this is the phenomenon which is generally known under the 
name of Indian Summer. It appears to be due to an uncom- 
‘monly tranquil condition of the atmosphere extending entirely 
across the continent; and similar cases frequently occur in 
each month of the year from September to March, but are 
most common in October. 
A comparison of all the facts which: have been presented in 
this paper, together with my six former papers, appears to 
warrant the following generalizations. 
. Areas of low barometer result from a general movement 
of the atmosphere towards a central area, and this movement 
1s accompanied by a deflection of the wind to the right, which 
causes a tendency to circulate around the center with a motion 
Brie | inward. 
of an inch. In these storms, three-quarters of the observed 
depression of the barometer is usually the effect of the earth’s 
