156 PHILOSOPHY OF STORMS. 



permost clouds are coming from the south west. Indeed, 

 these north east storms are frequently announced, not only 

 by a sudden rise of the barometer, as just mentioned, but 

 by a hazy cloud rising in the south west opposite to a north 

 east wind. 



125. When a summer storm passes in sight, note the phe- 

 nomena. Not unfrequently the barometer rises in the bor- 

 ders of the storm, and, during the rain or hail, the wind 

 blows outwards from the centre of the shower. It is very 

 desirable to know to what distance this outward wind and 

 rise of the barometer reach, and what effect it has in gene- 

 rating new clouds, by the warm moist air blowing up over 

 it. The dew point frequently falls by this outspreading of 

 the air below, reaching an observer at some distance from 

 a rain, and thus becomes a forerunner of an approaching 

 shower, generated in the manner indicated above. 



If a mountain were suddenly elevated by volcanic agency 

 across our country from north west to south east, it would 

 become the immediate cause of rain, by the air rising up 

 over it as it blows from the south west. Every thunder 

 shower produces a mass of cold heavy air, through which 

 the drops of rain or hail have passed, tending to produce a 

 new shower on the windward side of this cold mass, just 

 as a mountain would do. To investigate all the phenomena 

 of this summer shower, forms no inconsiderable part of our 

 present object. I hope next year, if Congress should this 

 winter lend their powerful aid to this important undertaking, 

 to be able to investigate our great north east winter storms 

 in like manner ; for our wide extended territory is peculiarly 

 suited to this investigation. At present, we neither know 

 the size nor the shape of these storms ; though the direction 

 in which they move, and their velocity, are better known 

 than those of any other storms, with the exception of the sum- 

 mer tornadoes, which nearly all move from the south west or 

 W. S. W. in this latitude. Indeed, it seems probable, that 



