334 Notes on Dust Whirlwinds and, Cyclones. [No. 4. 



hottest hours of the day, it would seem that the solar influence may 

 be considered at least a subordinate cause in bringing them into action. 



8. — The winds caused by the passage of whirlwinds, or electro- 

 magnetic spirals through the air, are characterized by gusts or flaws, 

 succeeded by lulls, and are of a totally different description from the 

 winds caused by variations in temperature, or by the rotation of the 

 earth on its axis. 



9. — The dust whirlwinds are usually composed of many single 

 spirals joined together ; these may separate and reunite again with 

 augmented power. 



10. — They preserve a distinct columnar form to the height of three 

 thousand feet and upwards, and terminate in a cloud of dust, which 

 still possesses a gyrating motion, ascending higher and higher. 



11. — A dust column or pillar of that height is sometimes observed 

 broken in its ascent into two or three lengthened irregular patches of 

 dust, with perfectly clear intervening spaces ; the dust all the while 

 ascending with rapidity into the higher regions, as if the electrically 

 charged pillar were endued at times with an increased centrifugal 

 force. 



12. — Their rate of upward ascent is subject to variation, as well as 

 their onward motion. 



13. — A lofty dust column, moving slowly, may sometimes be seen 

 to assume, in the course of a few seconds, a wavy, and slightly con- 

 torted appearance in its vertical section, while still preserving its exact 

 cylindrical form ; the change being effected simultaneously throughout 

 its entire height. 



14. — Kites, (which are numerous in this part of the country) often 

 follow the dust whirlwinds for some distance, soaring about and around 

 it, diving at each other, as if in sport ; and, seemingly, with no other 

 purpose, than that of enjoyment. 



15. — Evaporation is much increased when the whirlwinds are fre- 

 quent and the wind brisk. 



16. — In damp weather, the passage of the electrical spirals over an 

 insulated wire, fails to affect the gold leaf electrometer — and during 

 this humid state of the atmosphere, the electrometer can only be 

 excited with difficulty, and loses power the moment the excitement 

 is removed. 



