I20 TRANS. ST. LOUIS ACAD. SCIENCE. 



liar "explosive action."* To illustrate : a one-story brick building (as at 

 13, D. 2), protected on the west, 20 ft. distant, by a tall substantially built 

 brick block; on the east, 20 inches, a one-story frame; and 15 ft. from the 

 last a two-story brick. Now the vortex struck the brick block on the west, 

 tearing off the roof and the west wall down to the second floor ; then, ris- 

 ing and inclining upwards, it took the brick partition and the east wall, the 

 latter extending nearly to the top of the second story; next passing over 

 13 & 14 (the one-story building), but striking the next brick building, and 

 cutting off the fire-wall above the roof. The line of destruction was evenly 

 and plainly marked, and the debris was scattered (some of it) a long dis- 

 tance. This line was above 13 & 14, and yet what was the result.' At 13, 

 the east wall leaned over at the top, resting against the west wall of 14, 

 20 inches distant; the northwest and south walls lay on the ground, as if 

 they had been evenly pushed over outwards, the roof attached to the upper 

 joists in their normal relation ; the east end of these joists rested on the 

 wall that leaned against the next building, and the west end rested on the 

 floor, which had not been moved ; no part or portion had been carried 

 away; the furniture and clothing all left and not scattered; two persons 

 under the leaning joists and roof uninjured. No. 14, built of wood, had 

 the gables burst outward, but again there was no scattering. 



In about thirty minutes after the vortex had passed, there was a return 

 current from the north, bearing a very severe hail and rain storm, accom- 

 panied by a most terrific electrical display. There was no electrical dis- 

 turbance — as would be indicated by lightning and thunder— connected, in 

 any manner, with the vortices. 



* This is sometimes attributed to rarefaction of air outside of the house, the unbalanced 

 internal pressure throwing the walls outward. To say, under the conditions which obtain 

 in a tornado, that there is a tendency to rarefaction at the centre of the vortex, is equivalent 

 to the statement that the wind is blowing. 



In case of a vortex approaching a building, the inrushing wind would cause a great 

 pressure on the windward side of the house, and the pressure on the lee side would be less. 

 The breaking of a window on the windward side would transmit the pressure to the inte- 

 rior. The support of the side walls would cause the lee wall to be most vulnerable. The 

 side walls might also be started outwards, and the reverse winds , after tlie tornado has 

 passed, would tend to throw the remaining walls outwards. The violence of the wind 

 would, of course, determine the distance to which the ruins would be scattered. 



F. E. N. 



