LABORS OF THE JOINT COMMITTEE. 145 



than the air on the outside of the cloud, for every hundred 

 yards above its basis. 



7. The specific gravity of the cloud will thus be less than 

 that of the air at the same height, a quantity which can be 

 calculated if the dew point and the height of the cloud are 

 given. 



8. The air in the cloud will therefore move upwards in 

 the middle, and outwards above, and inwards below, with 

 a depression of the barometer under the cloud, and a rise 

 all round the cloud, produced by the outspreading of the air 

 above. 



9. If the depression of the barometer is given, the velocity 

 of the upward motion will be known, at least in the case of 

 tornadoes or spouts. 



10. If the velocity of upward motion is known, the quan- 

 tity of vapor condensed in a given time is known. 



11. The commencement of this upward motion may de- 

 pend either on a higher temperature, or a higher dew point 

 than in surrounding regions. 



12. The barometer would probably rise more on the north 

 east side of the storm than on any other side, on account of 

 the general motion of the upper portion of the atmosphere, 

 being towards the north east in this latitude. 



P. S. A journal of the weather for the month of March, 

 1838, was kept at St. Mary's College, Frederick Co., (Md.) 

 by Professor Elder, and it appears by it that the wind was 

 very violent all day on the 17th, from north west to north, 

 with but little depression of the barometer, l-10th inch from 

 the 16th. 



The wind on the 18th was still very strong N. N. W., and 

 it did not entirely cease snowing till about two o'clock. Mr. 

 Elder thinks if it had been all snow and no rain, it would 

 have been three feet deep. 



I have also received a letter from Professor G. W. Keely, 

 of Waterville, Maine, from which it appears that the wind 



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