E. Loomis — Contributions to Meteorology. 255 



discordances which may be partly due to the different modes 

 of comparison which have been adopted. In No. 1 a center of 

 low pressure was compared with the station of greatest rain-fall 

 when the rain-fall amounted to at least 2-J- inches in 8 hours. In 

 No. 2 a center of low pressure was compared with the station of 

 greatest rain-fall, when the rain-fall amounted to at least 2 

 inches in 8 hours. In No. 5 a center of low pressure was com- 

 pared with the station of greatest rain-fall, when the rain-fall 

 amounted to at least 2-| inches in 24 hours. In No. 3 a center 

 of low pressure was compared with the station of greatest rain- 

 fall, when the total rain-fall at all the stations east of the Rocky 

 Mountains was unusually great. In No. 1± the amount of rain- 

 fall is entirely unknown, but the center of a great rain area was 

 compared with the center of a neighboring area of low pres- 

 sure. 



The principal discordances in the preceding results cannot 

 be ascribed to the different modes of comparison adopted, but 

 must be due to some other cause. The great excess of rain 

 centers on the east side of the low center in No. 3 may reason- 

 ably be ascribed to the influence of the Atlantic Ocean with its 

 Gulf Stream, furnishing an inexhaustible supply of vapor ; and 

 the comparatively small number of rain centers on the east 

 side of the low center in Europe may be ascribed to the influ- 

 ence of the dry air in the interior of the continent. 



18. The preceding results have been derived from a com- 

 parison of rain-falls of unusual magnitude. It is not safe to 

 conclude that the same results would be derived from a com- 

 parison of the aggregate rain-fall for an entire year at each 

 station, since small rain-falls may be subject to a law somewhat 

 different from those of extraordinary magnitude. There is 

 another mode of comparison which takes account of the total 

 rain-fall at any station. Generally on the preceding side (which 

 is usually on the eastern side) of a low center, the barometer is 

 falling, and on the following side (which is usually the western 

 side) the barometer is rising. The mode of comparison con- 

 sists in determining the total amount of rain which comes dur- 

 ing a year with a falling barometer, and also that which comes 

 with a rising barometer, and finding the ratio of these two 

 amounts. 



19. In my 12th paper I gave the results of this mode of com- 

 parison derived from the best materials which I was able to 

 obtain. More recently I have extended the comparison to 

 Pawlowsk near St. Petersburg ; to Brussels for an entire year ; 

 to Aberdeen for two years ; and I have included the observa- 

 tions of two years at Indianapolis, Indiana. These last obser- 

 vations were derived from the Signal Service, the rain being 

 measured three times a day. The time of least pressure was 



