254: E. Loomis — Contributions to Meteorology. 



is unexpectedly prevalent over the Atlantic Ocean ; there be- 

 ing 38 cases in which the rain center was associated with a 

 pressure above 30 inches ; 17 cases in which the rain center 

 was associated with a pressure above 30*1 inches ; and 5 cases in 

 which the rain center was associated with a pressure above 30*2 

 inches, the highest being 30*4 inches. There were also 25 

 cases (group E) in which the rain was about equally divided 

 between areas of high and low pressure. Similar cases some- 

 times occur in the United States, where great rain areas fre- 

 quently extend somewhat beyond the isobar 30 inches. 



Two-thirds of the cases included in group 6r were so near to 

 the Gulf Stream that this stream may be presumed to have had 

 an important influence on the rain-fall. The live cases in which 

 the rain center was associated with a pressure exceeding 30'2 

 inches were all near the Gulf Stream, and appear to have been 

 similar to cases in the United States. 



We see that over the Atlantic Ocean the air does not always 

 descend from the upper regions over every part of an area of 

 high pressure. Over some portion of an area of high pressure, 

 the air frequently ascends ; and this appears to take place 

 when the air contains an unusual amount of aqueous vapor. 



17. A comparison of the results now obtained suggests 

 some important conclusions respecting the influence of local 

 causes in modifying the relation of rain-fall to barometric pres- 

 sure. We have found that in the United States, east of the 

 Rocky Mountains, — 



1. South of Lat. 36°, a rain-fall of 2-| inches in 8 hours at 

 any station occurs on the east side of a low area more fre- 

 quently than on the west side, in the ratio of 2*6 to 1. 



%. North of Lat. 36°, a rain-fall of 2 inches in 8 hours at any 

 station occurs on the east side of a low area more frequently 

 than on the west side, in the ratio of 2 - 8 to 1. 



3. A total rain-fall of 9 inches in 8 hours at all the stations 

 east of the Rocky Mountains occurs on the east side of a low 

 area more frequently than on the west side, in the ratio of 6*2 

 to 1. 



4-. Over the North Atlantic Ocean great rain areas occur on 

 the east side of an area of low pressure more frequently than 

 on the west side, in the ratio of 2*6 to 1. 



5. In Europe a rain-fall of 2|- inches in 24 hours at any station 

 occurs on the east side of a low area more frequently than on 

 the west side, in the ratio of 2*0 to 1. 



These results indicate that in the United States and Europe, 

 as well as over the North Atlantic Ocean, great rain-falls are 

 generally associated with a barometric pressure somewhat be- 

 low the mean, and the precipitation occurs chiefly on the 

 eastern side of a low area. We notice, however, considerable 



