238 HISTOR1 OF 



thence.' For this reason our easterly winds that blow from the 

 continent are diy in comparison of those that blow from the sur- 

 face of the ocean, with which we aie surrounded on every other 

 quarter. 



In general the winds are more boisterous in spring and 

 autumn than at other seasons : for that being the time of high 

 tides, the sea may communicate a part of its motions to the 

 winds. The sun and moon, also, which then have a greater ef- 

 fect upon the waters, may also have some influence upon the 

 winds : for there being a great body of air surrounding the globe, 

 which, if condensed into water, would cover it to the depth of 

 thirty-two feet, it is evident that the sun and moon will, to 

 a proportionable degree, affect the atmosphere, and make a tide 

 of air. This tide will be scarcely perceivable, indeed; but, 

 without doubt, it actually exists ; and may contribute to in- 

 crease the vernal and autumnal storms, which are then known to 

 prevail. 



Upon narrowing the passage through which the air is driven, 

 both the density and the swiftness of the wind is increased. 

 For, as currents of water flow with greater force and rapidity by 

 narrowing their channels ; so also will a current of air driven 

 through a contracted space, grow more violent and irresistible. 

 Hence we find those dreadful storms that prevail in the defiles 

 of mountains, where the wind, pushing from behind through a 

 narrow channel, at once increases in speed and density, levelling 

 or tearing up every obstacle that rises to obstruct its passage. 



Winds reflected from the sides of mountains and towers, are 

 often found to be more forceful than those in direct progression. 

 This we frequently perceive near lofty buildings, such as churches 

 or steeples, where winds are generally known to prevail, and thai 

 much more powerfully than at some distance. The air in this 

 case, by striking against the side of the building, acquires addi- 

 tional density, and, therefore, blows with more force. 



These diflferent degrees of density, which the air is foimd to 

 possess, suificiently show that the force of the winds do not 

 depend upon their velocity alone ; so that those instruments 

 called anemometers, which are made to measure the velocity oi 

 the wind, will by no means give us certain information of the 



i Derham'o I'liysini-Theoi. 



