E. Loomis — Contributions to Meteorology . 245 



States, is not very great, and may disappear in a longer series 

 of observations. 



These great rain-falls occur somewhat more frequently near 

 the coast of the Atlantic or the Gulf of Mexico than at interior 

 stations. Of the 67 cases compared, 46 occurred on or near 

 the coast, and 21 occurred at interior stations. During the 

 period of these observations, the number of coast stations was 

 somewhat greater than the interior stations, and the average 

 number of great rain-falls at the coast stations was about one- 

 half greater than at interior stations. 



The rain center was generally on the east side of the low 

 center, and the number of cases for each of the four quadrants 

 was as follows : 



Kain center in the N.E. quadrant, 34 per cent of the whole number. 



S.E. " 21 " " " 



N.W. " 5 



S.W. " 18 



The two centers coincident, 22 " " " 



The most noticeable difference between these results and 

 those for the northern portion of the United States is a less 

 number of cases in the S.E. quadrant, and a greater number in 

 the S.W. quadrant. This difference may perhaps be ascribed 

 to the fact that in the southern portion of the United States^ 

 the Gulf of Mexico is an important source of the vapor which 

 is precipitated, while in the northern portion, the Atlantic 

 Ocean affords the principal supply. 



Among the 67 cases under examination, there is only one case 

 in which two and a half inches of rain fell in two successive 

 periods of eight hours at the same station, and there are three 

 other cases in which two and a half inches fell in a second period 

 of eight hours at a station near the first. Thus we see that while 

 heavy rains are of more frequent occurrence in the southern 

 part of the United States than they are in the northern part, 

 they have a less period of duration. 



The depression of the barometer accompanying great rain- 

 falls is not very great, the average pressure at the low center 

 being 29*63 inches for that part of the United States north of 

 Lat. 36° ; and 29 77 inches for that part of the United States 

 south of Lat. 36°. 



4. In order to show what effect is produced upon the rain- 

 fall by an extraordinary depression of the barometer, I have ex- 

 amined all the cases in which the barometer fell below 29 

 inches, at any station in the United States or Canada, during 

 the period from September, 1872, to June, 1884. The num- 

 ber of such cases is 131, and the average rain-fall in 24 hours 

 at all these stations was l - 58 inches, and the greatest rain-fall at 

 any of the stations was 4*32 inches. At 38 of the stations the 



