142 ON THE STORM EXPERIENCED THROUGHOUT THE UNITED STATES 



Here is exhibited no oscillation of the barometer; but a mean depression of 

 the thermometer, on the 20th, of three degrees from the 19th, and 4°.7 from the 

 18th. This was simultaneous with the depression of the thermometer at the 

 most, western stations of the United States. It should be remembered, also, 

 that although this fall of temperature was slight, it was considerable for the 

 latitude. On the 19th the wind was south-east, with rain. The coincidence 

 is certainly remarkable. Although, then, it seems not improbable that the 

 causes which, in the United States, were operating with such energy, were 

 sensible even in the vicinity of the equator, still, as there was no fall of the 

 barometer, and the depression of the thermometer was but slight, we shall hesi- 

 tate to call it the same storm, and shall fix upon the parallel of 25° N. latitude 

 as being not far from the southern limit of our storm. I have received a copy 

 of the observations made on board the United States ship Erie, at Buenos 

 Ayres, during the month of December, 1836, but it is impossible to identify 

 any movement of the barometer from observations at a single station so remote. 



The boundary on the west must be somewhat conjectural. At the rate with 

 which the storm moved across the western states, it would have travelled from 

 the Rocky Mountains to Fort Leavenworth in sixteen hours. The depression 

 of the thermometer was more sudden and greater in amount at the western sta- 

 tions than in any other part of its observed course. No reason, then, can be 

 seen why the storm should not have extended to the Rocky Mountains. But 

 could it pass them? These mountains, in connexion with the Cordilleras, are 

 understood to form a continuous range from the Frozen Ocean to the interior 

 of Mexico, every where several thousand feet in elevation, and presenting insu- 

 lated peaks, which, according to Professor Renwick, attain the height of 

 twenty-five thousand feet above the sea. Suppose the warm south-east wind 

 which was felt in the United States to blow over this wall covered with per- 

 petual snow. The temperature of those elevated peaks during the month of 

 December can hardly be supposed equal to zero of Fahrenheit. This warm 

 current would then be suddenly cooled down to the temperature of that eleva- 

 tion, and its moisture be precipitated. The eastern side of the mountain would 

 be buried in snow. Suppose the same air to continue its course and descend 

 upon the other side of the range. It now comes into a warmer region; it 

 brings with it only the moisture proper to an exceedingly low temperature; it 

 is therefore a cold and dry wind, instead of a moist and warm one. Its cha- 



