368 Report on the Dust Whirlwinds* [No. 4s 



the wind must have from E. to L. it is nevertheless a matter of 

 considerable difficulty to say positively whether they were true 

 cyclones. It certainly may be that the motion of the wind in them 

 was rectilinear, although from the visible bearing of their mass, 

 the direction of the wind is readily accounted for by supposing 

 them to have been circular. It appears to me that in order properly 

 to ascertain the nature of these and similar land storms, it is abso- 

 lutely necessary that a cordon of observers be established at various 

 stations, for this purpose. 



From the above two slight storms, we readily draw the deduction 

 that, 



a. It is at times difficult, if not impossible, for a single observer 

 to decide whether the motion of the wind in certain storms is 

 rectilinear or circular. 



10 and 1 1.-30^ March, 1853. At sunset of 29th, the sky ge- 

 nerally was much covered with cumuli and strati, the setting of the 

 sun giving the horizon in the W. a red lurid appearance. The morn, 

 mg of the 30th was hazy ; atmosphere close and still, yet a quantity 

 of impalpable dust was suspended in it. About 10 a. m. a sharp 

 breeze occurred from S. and from the darkness to W. and N. at 

 that time, it would appear that the circular motion of the wind was 

 from E. to L. and that the border of the circle only passed over 

 the cantonments. The breeze soon diminished in intensity, but the 

 atmosphere continued hazy, and the temperature was considerably 

 lowered. At 6 p. M. a dark mass of cloud and dust was observed 

 in the N. and N. W. extending to about N. E. It rapidly advanced 

 and then struck our house at N. by E. ; varying between this point 

 and N. 



It was interesting to observe spiral columns of dust such as are 

 <ZH>\ <0< represented in the margin coming along 



C^< C^< w ^k anc ^ f ac i n g P ar t of the body of the 



p^ j S<i storm, the convexity of their course being 



<^ ^^ forward, and the gyrations of the minor cur- 



rents of wind of which they seemed to be constituted having a direc- 

 tion from L. to E. and extending upwards from the ground into the 

 atmosphere, and with an onward progress such as would be repre- 

 sented by an imaginary horizontal section near the earth, thus 



