CYCLONIC WINDS. 99 



This fourth movement existing in a tornado might not 

 constantly manifest itself, for when obstructions are en- 

 countered, the general movements are disturbed, and the 

 circular ones raised from earth contact. But when there 

 are no serious obstructions the surface air is enabled to flow 

 in freelj^ and fully and produce a complete C3'lindrical move- 

 ment, then, and following such an attained condition, should 

 occur manifestations of this fourth movement. 



