230 ruir.osoruv of storms. 



(lejrrces for every iucli which the barometer stands lower under the 

 cloud than on tlie outside. This expansion and refrigeration of the air 

 will, under tliesc circumstances, occur immediately upon its ingress 

 under the cloud, apart from the influence exerted by its ascent. 



In consequence of this reduction in temperature from diminished 

 pressure, the air will not have to ascend so high before it begins to con- 

 dense its vapor, as it did when the cloud began to form at first, and 

 consequently the cloud will be formed lower and lower by the ascend- 

 ing column, in proportion as it increases in perpendicular height from 

 its base to its top. The difference between our assumed dew-point and 

 temperature being 10 degrees, the height of the base of the cloud at its 

 first formation will be 1000 yards, but as every^ inch of depression of the 

 barometer produces 5 degrees of cold, the difference between the dew- 

 point and temperature will be reduced correspondently. Consequently 

 if the barometer fall? one inch, this difference will be only five degrees, 

 which being the complement of the dew-point, the condensation of va- 

 por must occur 500 yards lower than at first, making the base of the 

 cloud- at this instant, only 500 yards high. A reference at this time to 

 the temperature of the dew-point will at once indicate this fact. 



The cloud becoming of greater perpendicular diameter, and the bar- 

 ometer sinking more and more under its base, in consequence of the 

 specific levity of the air in the cloud, and this being a cooling process, 

 the temperature of the air below the cloud is rapidly reduced down to the 

 temperature nearly of the dew-point. The air, therefore, not only expands 

 and cools so soon as it comes under the cloud, but cloud may begin to 

 form so soon as the air comes into the centre of the ascending column, 

 even before it has left the surface of the ground, and thus the cloud will 

 touch the earth. 



If the cloud now be narrov/ and very lofty lift strife of elements 

 })ccomes intense. With a mighty steam-power, it sweeps, with mighty 

 grai;deur, across the sea, or, in the majesty of its might, drives its im- 

 petuous career over the earth, at once prostrating, with unrelenting fury, 

 the firmly rooted monarchs of the forest, and desolating the strongest 

 and proudest architectural monuments of juan. Well may the Psalmist 

 .say that '*the voice of the Lord is upon the waters !" that lie "shaketh 

 the wilderness!" that He "rides upon the wind, and directs the storm !" 



I will endeavor to illustrate this part of the subject by detailing the 

 phenomena that usually occur in the forming-stage of these violent 

 storms. If we are upon a mountain when those clouds called cumuli. 

 are forming over a plain, we will perceive that their bases are all upon 

 the same level. Should the dew-point be very high, and everything 



