E. Loomis — Contributions to Meteorology. 253 



This I have derived, from the Atlantic Weather Charts from 

 Aug. 1, 1882, to Sept. 3, 1883, published under the authority 

 of the British Meteorological Council. These maps show for 

 each day the region where showers prevailed and where rain 

 prevailed. I have selected all the cases in which there is 

 marked upon these maps a rain area more than 600 English 

 statute miles in length, omitting the tropical regions. The 

 number of these cases is 375. In order to exhibit more clearly 

 the -character of the results, I have divided the cases into seven 

 groups. Group A contains 29 cases in which the center of the 

 rain area coincided nearly with a center of low pressure ; group 

 B contains 161 cases in which the rain was associated with an 

 area of low pressure, chiefly on its eastern side ; group C con- 

 tains 46 cases in which the rain center was almost exactly 

 north or south of a center of low pressure ; group D contains 

 51 cases in which the rain was associated with an area of low 

 pressure chiefly on its western side ; group E contains 25 cases 

 in which the rain was partly over an area of low pressure, and 

 partly over an area of high pressure, being about equally 

 divided between them ; group F contains 22 cases in which the 

 rain-fall was accompanied by a barometric pressure above 30 

 inches, and the rain area was situated between two areas of 

 high pressure ; and group Gr contains 38 cases in which the rain 

 fell chiefly over an area of high pressure, and was not distin- 

 guished by the peculiarity of group F. 



15. These great rain areas are found in all months of the 

 year. The distribution by seasons is as follows : Winter, 74 ; 

 Spring, 128 ; Summer, 78 ; and Autumn, 78 ; showing that 

 over the North Atlantic Ocean, great rains occur most fre- 

 quently in the spring of the year, especially in the month of 

 March. 



These rain areas sometimes have very great extent, there 

 being 120 cases in winch the rain area was at least 1000 Eng- 

 lish statute miles in length ; 29 cases in which it was at least 

 1500 miles in length ; 8 cases in which it was at least 2000 

 miles in length ; and 5 cases in which the rain area was over 

 2500 miles in length. 



The number of rain areas associated with areas of low pres- 

 sure, chiefly on the eastern side (group B) is 161 ; and the 

 number chiefly on the western side (group D) is 51. The 

 former number is three times the latter. If, however, in this 

 comparison we include group A, and consider half of these 

 cases as situated on the east side of the low center, and the 

 other half on the west side, we shall have on the east side 176 

 cases and on the west side 68 cases ; which numbers are in the 

 ratio of 2*6 to 1. 



16. Rain, with barometric pressure somewhat above 30 inches, 



