Observations of the United States Signal Service. 19 



one mile per hour; in two cases it was four miles per hour ; in 

 one case it was five miles; in one case eight miles and in one 

 case twelve miles per hour. We thus see that during a heavy 

 rain-fall, the wind either blows from some eastern quarter, or 

 its velocity is almost invariably small. 



At the northern stations there are but eight cases in which 

 east winds are not reported either at date or at the preceding 

 observation. These exceptions are Nos. 2. 12, 16, 18, 20. 21, 

 28 and 29. Two of these cases occurred on the summit of Mt. 

 Washington; in one of the remaining cases the velocity of the 



twelve miles per hour. We thus see that at the northern sta- 

 tions as well as at the southern, during a heavy rain-fall the 

 wind blows from some eastern quarter, or its velocity is almost 

 :v small. 



On Plate III are shown the curves of equal rain-fall for 

 Sept. 23, 1872, being No. 1 of the table on page 15. The outer 

 curve shows the extreme limits of the rain area and the other 

 curves show the limits of a rain fall of one inch and of two 

 inches. The arrows show the direction of the wind at 7 A. M., 

 which was previous to the middle of the rain fall. There was 

 a center of lo v pn ssun cli'So) near Omaha, which was about 

 west of the center of the rain area and distant from it 660 miles. 

 Near the Atlantic coast there was a belt of high pressure 

 (80-25). The result of this unequal pressure was a general 

 prevalence of southeast winds throughout a large part of the 

 Mi«i—q>pi valley. Northerly winds commenced blowing from 

 the neighborhood of Lakes Superior and Huron, being the 

 result of a lower temperature and a higher pressure. This 

 colder wind from the north probably flowed under the math- 

 east wind which had been blowing over Luke Michigan and 

 produced that strong upward movement of the air which was 

 followed by excessive rain at Grand Haven una Milwaukee. 



In a large number of the cases in the tabic on page 15 the 

 observations show that a southeast wind at certain stations was 

 opposed by a westerly or northerly wind at other stations. 

 This opposition or interference of winds generally results in a 



a movement in nearly all of the cases in the table on page 15. 

 When the ra ' ' from the center of low pressure 



md lid not generally exert a decided influence upon the 



In preparing the materials for this article I hav 



