256 E. Loomis — Contributions to Meteorology. 



determined from the tri-daily weather maps, and the rain was 

 accordingly distributed under the two heads of falling and ris- 

 ing barometer. This method cannot give accurate results, but 

 may furnish useful information in the absence of hourly obser- 

 vations. By grouping together those stations which seem most 

 intimately related, we obtain the following results, showing the 

 ratio of the amount of precipitation which comes with a falling 

 barometer, compared with that which comes with a rising 

 barometer. 



Indianapolis, Ind., ratio, 1*32 to 1 

 Philadelphia, Penn., " 2-88 to 1 

 Seven British stations, " 2*08 to 1 

 Paris and Brussels, " 1*19 to 1 



Pawlowsk, Russia, " 1-06 to 1 



Prague and Vienna, " 0- 80 to 1 



20. These results exhibit a remarkable accordance, and indi- 

 cate the operation of a general cause. They are similar to 

 those previously stated, but are much more definite. At Phila- 

 delphia the amount of rain which falls while the barometer is 

 descending is nearly three times as great as that which falls 

 while the barometer is rising ; and during the six colder months 

 of the year, the rain-fall in the former case is nearly five times 

 as great as in the latter case. In summer, thunder showers 

 frequently occur with an abundant fall of rain accompanied by 

 a slight rise of the barometer, and at such times there is more 

 rain with a rising than with a falling barometer. The entire 

 Atlantic coast of the United States, JNorth of Lat. 36°, exhibits 

 results similar to those found for Philadelphia. 



As we proceed westward from the Atlantic coast, the ratio 

 of the precipitation when the barometer is falling, compared 

 with that when the barometer is rising, changes somewhat 

 rapidly, and before we reach the Mississippi River the ratio is 

 reduced to 1*32. These results indicate that the great excess of 

 rain on the eastern side of areas of low pressure near the At- 

 lantic coast is due to the fact that on the eastern side they 

 have the Gulf Stream, which furnishes an inexhaustible supply 

 of vapor. 



In Great Britain the amount of rain with a falling barometer 

 is twice that with a rising barometer ; but as we proceed east- 

 ward this ratio diminishes rapidly, and in Central EurojJe the 

 precipitation is greater when the barometer is rising, than when 

 the barometer is falling. This result is due to the fact that 

 in Central Europe, areas of low pressure have a comjmratively 

 dry air on their eastern side, and there is a more liberal supply 

 of vapor on the western than on the eastern side. Hence we 

 conclude that the amount of rain-fall on the eastern side of an 

 area of low pressure depends largely upon the direction and 

 distance of the principal supply of aqueous vapor. 



