TKllRESTItlAL HEAT. 



hall. A plunk of wood 3| feet long, 9 inches wide, and an incli 

 thick, was projected with such force as to cut through a branch of 

 palm wood 18 inches in diameter. A piece of wood 15 feet long 

 and 8 inches square in its cross section, was projected upon a 

 hard paved road, and buried to a depth of more than three feet 

 in it. A strong iron gate in front of the governor's house was 

 carried away, and three twenty-four pounders erected on the fort 

 were dismounted. 



58. These effects, prodigious as they are, all arise from mechani- 

 cal causes. There is no agent engaged in hurricanes more subtle 

 than the mechanical force of air in motion, and since the weight 

 and density of the air suffer no important change, the vast momen- 

 tum manifested by such effects as those described above, must be 

 ascribed altogether to the extraordinary velocity imparted to the 

 air by the magnitude of the local vacuum produced, as already 

 stated, by the sudden condensation of vapour. To form some 

 approximate estimate of this it may be observed that, in the inter- 

 tropical regions, a fall of rain often takes place over a vast extent 

 of surface, sufficient in quantity to cover it with a stratum of 

 water more than an inch in depth. If such a fall of rain were to 

 take place over the extent of a hundred square leagues, as some- 

 times happens, the vapour from which such a quantity of liquid 

 would be produced by condensation would, at the temperature of 

 only 50, occupy a volume of 100000 times greater than that of 

 the liquid: and, consequently, in the atmosphere over the surface 

 of 100 square leagues it would fill a space 9000 feet, or nearly two 

 miles in height. The extent of the vacuum produced by its con- 

 densation would be a volume nearly equal to 200 cubic miles, or 

 to the volume of a column whose base is a square mile and whose 

 height is 200 miles. 



59. The phenomena, called water or land spouts according as 

 they are manifested at sea or on land, consist apparently of dense 

 masses of aqueous vapour and air, having at once a gyratory and 

 progressive motion, and resembling in form a conical cloud, the 

 base of which is presented upwards, and the vertex of which 

 generally rests upon the ground, but sometimes assumes a contrary 

 position. This phenomenon is attended with a sound like that of a 

 waggon rolling on a rough pavement. 



Violent mechanical effects sometimes attend these meteors. 

 Large trees torn up by the roots, stripped of their leaves, and ex- 

 hibiting all the appearances of having been struck by lightning, 

 are projected to great distances. Houses are often thrown down, 

 unroofed, and otherwise injured or destroyed, when they lie in the 

 course of these meteors, llain, hail, and frequently globes of fire, 

 like the ball lightning, also accompany them. 

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