16 K Loomis— Results derived from an examination of th 



greatest rain-tall v 

 amount of the ra 

 barometer at the same station ; column 6th shows the directioi 

 and force of the wind at the last preceding observation ; column 

 7th shows the direction and force of the wind at the date given 

 in column 2d ; column 8th shows the direction of the rain 

 center from the nearest center of low pressure ; column 9th 

 shows the distance of the rain center from the center of low 

 pressure, expressed in miles; and column 10th shows the 

 height of the barometer at the center of low pressure. 



In all of these cases there was an area of low pressure within 

 the limits of the United States, and generally the place of 

 greatest rain-fall was within the cycloidal movement attending 

 this low pressure. The distance of the rain center from the 

 center of low pressure was however very variable. 





In the two cases of July 27th, the low pressure was so incon- 

 siderable and remote as to exert very little influence upon the 

 winds at Philadelphia and Washington. 



We thus see that norih of lat 36° great rain-falls generally 

 occur within 250 miles of a center of low pressure, and almost 

 invariably on the east side of the low center. In two of the 

 preceding cases (Nos. 12 and 31) the rain center is stated to be 

 west of the low center. But it should be remembered that the 

 rain-fall occurred during the eight hours preceding the date 

 of the barometric observation. The middle of the rain-fall may 

 be regarded as corresponding to a date four hours preceding 

 the barometric observation, and during these four hours, the 

 low center generally advances eastward 100 miles. We may 

 therefore conclude that in No. 31 the principal rain-fall occurred 

 when the rain center was east of the low center. In No. 12 the 

 prim i i i i n c urred on the southwest side of the low cen- 



ter, but the barometric gradient was only one-tenth of an inch 

 to 350 miles. The rain center occurs as frequently in the N.E. 

 quarter from the low center as it does in the S.E 'quarter. 



The four cases in which the rain center was more than 750 

 miles distant from the nearest center of low pressure were Nos. 

 6, 11, 20 and 21. In No. 6 a distinct local cyclone formed 

 near New York, accompanied by a slight local depression of 

 the barometer, which had the effect of urging the low center 

 eastward with extraordinary velocity. From 7.35 A.M. to 4.35 

 p.m., that is, in nine hours, the low center advanced eastward 

 900 miles, although the greatest velocity of the wind, recorded 



