;96 



NATURE 



[July i8, 1918 



east with tlie speed of a fast train (twenty to forty 

 miles an hour or more), its wind velocities exceeding 

 100, 200, and probably sometimes 300 or more miles 

 an hour ; its path of destruction usually less than a 

 quarter of a mile wide ; its total life a matter of 

 perhaps an hour or so. It is as ephemeral as it is 

 intense, 



Fortunately for man, tornadoes are short-lived, 

 have a very narrow path of destruction, and are by 

 no means equally intense throughout their course. 

 Their funnel cloud, which indicates the region of 

 maximum velocity of the whirling winds, ascends and 

 descends irregularly. Where it descends, the destruc- 

 tion is greatest; where it rises, there are zones of 

 greater safety. The whirl may be so far above the ground 

 that it does no injury whatever. It may descend low 

 enough to tear roofs and chimneys to pieces. It may 

 come down to the ground and leave "nothing standing. 



attested explosive effect accounts for many tornado 

 " freaks " which cannot be explained by any controls, 

 either of radially or spirally inflowing winds, whatever 

 their velocity. 



The damage done by tornadoes may be roughly 

 classified as follows : — (i) That resulting from, the 

 violence of the surface winds, blowing over buildings 

 and other exposed objects, crushing them, dashing 

 them against each other, etc. ; (2) that caused by the 

 explosive action ; and (3) that resulting from the up- 

 rushing air movement close around the central vortex. 

 Carts, barn-doors, cattle, iron chains, human beings 

 are carried through the air, whirled aloft, and dashed 

 to the ground, or they may be dropped gently at con- 

 siderable distances from the places where they were 

 picked up. Iron bridges have been removed from 

 their foundations ; beims are driven into the ground ; 

 nails are forced head-first into boards ; cornstalks are 



May 27, 1896. Wreck of Car Barn. From the Quarterly Journal of the Royal Meteorological Society. 



Damage and Loss of Life in Tornadoes. — The cen- 

 tral low-pressure core of the tornado is surrounded 

 by radially inflowing winds of moderate strength, and 

 then, closer to the centre, by spiralling and ascending 

 winds of terrific violence ; strong enough to crush and 

 wreck the strongest buildings ; ascending with suflfi- 

 cient velocity to carry aloft objects so heavy that for 

 wind to lift them seems almost impossible. The sur- 

 face winds which take part in the vorticular inflow 

 and ascent seem to be chiefly responsible for the 

 damage and loss of life. There is, however, an addi- 

 tional factor. The central " core," surrounded by its 

 whirling winds, has its pressure greatly reduced by 

 the centrifugal force of the whirl. It therefore exerts 

 a powerful explosive effect upon near-by air at ordinary 

 pressures, within buildings or in other more or less 

 well-enclosed spaces. This curious but very widely 

 NO. 2542, VOL. lOl] 



driven partly through doors ; harness is stripped from 

 horses ; clothing is torn from human beings and 

 stripped into rags. The damage is greater and ex- 

 tends farther from the centre on the right of the 

 track than on, the left, for the wind velocities are 

 greater on the* right, as in the "dangerous semi- 

 circle " on the right of the track of tropical cyclones. 



The explosive effects are many and curious. The 

 walls of buildings fall out, sometimes letting the roof 

 collapse on to the foundations ; or the roof may be 

 blown off, leaving the walls standing. The accom- 

 panying photograph (Fig. i) illustrates some of the 

 damage which was done by the St. Louis, Mo., tor- 

 nado of May 27, 1896. The surface of the ground may 

 be swept clean, as if with a broom. Articles may be 

 blown out of houses and carried to great distances. 

 Empty bottles are uncorked; feathers plucked from 



