376 Report on the Bust Whirlwinds. [No. 4. 



noting the wind point at each of the three observations as indicated 

 in the diagram. 



b. That the onward course or track of the storm was zig-zag. 



19. — \6th June, 1853. On 15th, and this forenoon there was a 

 general haze apparently from impalpable dust. Thermometer in the 

 house ranged to 98° F. At 3, 30 p. m., slight thunder was heard 

 overhead, and a dark cloud of dust was perceptible, occupying the 

 horizon from N. E. to N. W. (about half an hour previous, a whirl- 

 wind revolving from R. to L. passed over my house, proceeded in a 

 curvilinear direction first N. and then W. to some adjoining houses 

 with which, in coming in contact, it broke up). The storm was 

 not very violent, the wind first came on from S. "W. and in about 

 half an hour was blowing from E. Yery heavy rain fell, and the 

 sky first cleared up in N. E. the mass of the storm being chiefly pro- 

 gressing to the W. 



From the above storm we learn two points, and which, it may be 

 noted are borne out by other observations, the results of which it 

 is not the object of this paper to discuss, namely, 



a. A loaded state of the atmosphere from impalpable dust often 

 proceeds the occurrence of a storm. 



b. A cyclone is sometimes preceded by whirlwinds of greater 

 or larger dimensions.* 



20. — \Sth June, 1853. According to notes taken at the time 

 I find that the moderation of temperature by which the above storm 

 was followed continued. During the forenoon of the 18th an 

 agreeable breeze continued to blow, but shortly before sunset (it 

 having been S. E.) it ceased, and a bank as if of impalpable sand 

 and cloud appeared on the horizon, extending from N. E to S. and 

 probably with a diameter of ten miles. 



It was evidently concave ; the N. E. extremity appearing to be 

 nearer to our house than the S. About | past 6 p. M. the dust came 

 up from N. E. as represented in chart VI. 1853, (Plate XXI.) and at 

 the same time the two extremities were distinctly seen approaching 

 each other as the body of the storm progressed. (This approximation 

 of the extremities is endeavoured to be represented in the segment 2 



* A chart of this storm was prepared during its prevalence, and marked V. 1S53, 

 but in consequence of its inaccuracy, I have omitted it here. C. A. G. 



