380 Report on the Dust Whirlwinds. [No. 4. 



meteors as observed in the plains, and at a considerable distance 

 from mountains, lakes or seas. 



1st. 



a. The circular motion of the atmosphere in cyclones may be 

 from L. to B». (in the northern hemisphere) as in Nos. 1 , 3, 5, 13 

 and 21. 



b. It may be from E. to L. or contrary to the motion of the 

 hands of a watch, as in 14, 18 and 20, and here I would observe 

 that cyclones having this description of circular motion would appear 

 from my small series of observations to be of less frequent occur- 

 rence than those of an opposite character, such as are generally 

 believed to prevail south of the equator. 



c. No circular movement of air can be detected in all storms, as 

 4 and 16. 



d. It becomes difficult or even impossible from observations 

 taken in only one locality to say positively, whether the current of 

 air in a storm is rectilinear or circular, or if the latter, in which 

 direction revolving, as 8 and 9, 14 and 15. 



e. The onward course or track of a storm may be in a direct line, 

 curvilinear or zig-zag, as in Nos. 10, II, 13, 14 and 18. 



f. The track of a storm cannot under all circumstances be de- 

 tected (on land) as in No. 15. 



2nd. 



a. The occurrence of storms in the plains during the hot season 

 is usually proceeded by the appearance of certain phenomena, as 

 strati in the W. 1 6 and i 7, a loaded state of atmosphere from im- 

 palpable dust, as 6 and 19. Spiral columns of dust, or whirlwinds 

 .revolving and progressing in independent directions, 12. 



b. They consist of revolving spirals, as shown in Nos. 10, 11 

 and 20. 



c. These spirals may under certain circumstances attain a pro- 

 gressive motion before, by their lateral extension, they have com- 

 pleted the cyclone, as in No. 20. Yet under certain other circum- 

 stances, a cyclone may not at its commencement have any onward 

 motion, as No. 3. 



d. In some cases it would seem that in storms the greatest force 

 of the wind occurs at inconsiderable heights from the surface of the 

 earth, as in Nos. 10 and 1 1. 



