-1859] WRITINGS OF JOSEPH HENRY. 299 



The tremendous ascensional power which is exhibited in 

 storms of this kind, although almost exceeding belief, is 

 nevertheless in accordance with the established dynamical 

 principle of the accumulation of momentum in cases of the 

 continued action of a constant force. We are all familiar 

 with the velocity given to an arrow by a simple propulsion 

 of the breath along the interior of a blow-gun. In this case 

 the air presses against the end of the arrow, at first with just 

 sufficient force to move it; but the momentum it has thus 

 acquired is retained, it receives another pressure from the 

 air, retains the effect of this, and so on, until it leaves the 

 other end of the tube with the accumulated momentum ac- 

 quired during its whole passage through the interior of the 

 gun. In the same way the air, as it approaches the uprising 

 column below, commences its ascent with an amount of mo- 

 mentum which is constantly increased by continued pressure 

 from behind. The ascensional momentum therefore becomes 

 so great as to furnish a ready explanation for all the exhibi- 

 tion of mechanical power which is so frequently witnessed 

 in storms of this character in our climate. On account of 

 the rarefaction of the air in the centre of the storm in cases 

 where it has passed directly over head, buildings are instantly 

 unroofed, the sides are thrown outward, as if by the action of 

 gunpowder, chests are broken open, and corks forced from 

 empty bottles, in which they have been tightly fitted. In 

 these cases the outward pressure being in part removed, the 

 unbalanced repulsive energy of the atoms of the air within 

 the edifice causes the outward explosion. The force of this 

 outward tendency will not be surprising when we reflect upon 

 the great pressure of the atmosphere in its normal state, 

 which is equal to more than 2,000 pounds on every square 

 foot of surface, and which frequently and suddenly experi- 

 ences a reduction of a twentieth part of at least this amount, 

 or in other words, of 100 pounds to the square foot — an un- 

 balanced force abundantly sufficient to produce the effects 

 we have mentioned. 



Dr. Hare attributed the violent upward motion of the air 

 in tornadoes to a peculiar electrical state of the atmosphere 



