tSE Forces that prodcce storms. 



63 



adjoining heavier air that then presses and rushes in succes- 

 sively to fill the comparative vacuum, must produce a hori- 

 zontal movement of air or a wind, the force and rapidity of 

 which veil! be proportioned to the degree of vacuum created. 



In the table that has been given, we have exhibited the 

 cooling of the atmosphere through reduction of incumbent 

 pressures, as it may be presumed to take place in a tropical 

 region, to the height of only four thousand eight hundred 

 yards, because, in air that was undisturbed by condensation, 

 the temperature of 32° or the freezing point was then 

 attained. But there is no reason that an ascending current 

 heated by condensation as it proceeded, and pressed upwards 

 by fresh air rushing from below, should stop in its ascent 

 when it had reached the height of four thousand eight hun- 

 dred yards. On the contrary, the tendency of such a current 

 when supplied with sufficient vapour, which becomes lighter 

 through being warmed, is to permit its being raised to far 

 greater heights, and the difference in the temperature of the 

 two adjoining columns of clear and of clouded air, as long as 

 condensation was proceeding, would still be the measure of 

 power with which the heavier column would force up the 

 lighter. In the following table this difference is shewn up to 

 a height of ten thousand yards : — 



