O PHILOSOPHY OF STORMS. 



only one-fourth of thirty inches, it will be then at a tem- 

 perature of one degree at the upper end, and will have con- 

 densed two-thirds of its vapor capable of heating the con- 

 taining air 50, and then, according to article 13, it will be 

 50 warmer than the surrounding air at that height. And 

 . as the vapor condenses more rapidly in the lower part of the 

 column than in the upper, the mean temperature of the 

 whole column may safely be taken at 25 above the sur- 

 rounding air; therefore, the mean temperature of the air 

 being about 32, the expansion of the columnar air will be 

 about ^y, which would cause the mercury in the barome- 

 ter to be depressed about one inch and a fifth, and cause a 

 velocity in the column upwards of two hundred and fifty- 

 six feet per second. 



15. The quantity of rain produced by the refrigeration of 

 this ascending column, would be five inches in one minute 

 and twenty seconds, if it were all to fall on a space equal 

 in area to the area of the column. This, however, could 

 seldom happen, as the drops of rain would be carried up- 

 wards to a height greatly beyond the region of perpetual con- 

 gelation, and thrown off at the sides in the form of hail 



16. The dew point in the above calculation was assumed 

 at 71 ; if it had been taken at 80, to which it sometimes 

 rises at Philadelphia, it would have been found that the 

 barometer would in that case descend one inch and nine- 

 tenths, and all the other effects would be proportionably 

 aggravated. 



17. It will readily be perceived that the air will spread 

 out more rapidly at the upper end of the column than it 

 runs in below, and thus, at some distance from the column, 

 especially in front of the storm at the surface of the earth, 

 the barometer will rise, and the effect of this will be to in- 

 crease the velocity of the ascending column, for which no 

 allowance is made in the preceding calculation. 



18. It will also be perceived, that the air under the col- 



