244 E. Loomis — Contributions to Meteorology. 



stations during the period of the observations, the ratio of the 

 number of the interior stations to the coast stations was varia- 

 ble ; but for the entire period, the former were nearly three 

 times as numerous as the latter ; showing that near the Atlantic 

 coast north of Latitude 36°, great rain-falls occur four times 

 as frequently as in the interior of the United States, east of 

 the Rocky Mountains. 



2. The rain-areas were generally associated with areas of low 

 pressure, and the rain center was generally on the east side of 

 the low center. The number of cases for each of the four 

 quadrants was v as follows : 



Rain center in the N.E. quadrant, 30 per cent of the whole number. 



S.E. " 28 



N.W. " 9 



S.W. " 9 " " " 



The two centers coincident, 24 " " " 



The greatest rains are generally associated with areas of low 

 pressure of only moderate depression. For the cases which 

 occurred during the winter months, the average height of the 

 barometer at the low center was 29-50 inches ; and for the 

 cases which occurred during the summer months, the average 

 height of the barometer at the low center was 29 '70 inches. 

 In only one case did the barometer sink as low as 29 inches, 

 although in the United States and Canada the barometer sinks 

 below 29 inches on an average 17 times annually, as indicated 

 by tri-daily observations. 



Generally a rain-fall amounting to two inches in eight hours 

 does not last more than eight hours, either at the same station 

 or at any neighboring station. Among the 106 cases com- 

 pared, there were only five cases in which two inches of rain 

 fell in two successive periods of eight hours at the same station, 

 and there were four other cases in which two inches of rain 

 fell in the succeeding eight hours at a second station so near 

 the first station, that the rain may be presumed to have fallen 

 at this rate uninterruptedly for sixteen hours or more. 



3. During the period of 41 months' observations, there were 

 67 cases in which there was a rain-fall of at least 1\ inches in 

 eight hours at stations east of the Rocky Mountains, and south 

 of the parallel of 36°. These cases were distributed by seasons 

 as follows : Winter, 4 ; Spring, 9 ; Summer, 22 ; and Autumn, 

 32. The greatest number of cases occurred in the autumn, 

 while north of Lat. 36° the greatest number occurred in sum- 

 mer. South of Lat. 36° the month of greatest frequency is 

 September, while north of Lat. 36° the month of greatest 

 frequency is July, but August shows an almost equal number 

 of cases. The difference therefore in the date of maximum 

 frequency for the northern and southern parts of the United 



