50 Mr. T. Belt on the Origin of Whirlwinds. 



wind of the sandy deserts of Africa, the dreaded Sinaoom. This 

 is the outlet of the heated air extending over the surface of the 

 dry desert. It is the presence of this heated stratum that 

 causes the singular delusion of the mirage. In it we may per- 

 ceive the couching simoom luring on the weary traveller with 

 false hopes of arriving at refreshing sheets of water, then rising 

 in its fury and overwhelming man and beast in a mound of 

 sand. Bruce, speaking of the whirlwinds of the African desert, 

 says, "We saw towards the north a number of prodigious pillars 

 of sand at various distances, sometimes moving with great velo- 

 city, sometimes stalking on with majestic slowness." Another 

 traveller had an opportunity of seeing one of these pillars cross- 

 ing the river Gambia from the Great Desert. It passed within 

 eighteen or twenty fathoms from the stern of their vessel, and 

 seemed to be about 250 feet in height. Its heat was sensibly 

 felt ; and it left a strong smell like saltpetre, which remained a 

 long time. 



It is, however, over the expanse of the wide ocean that we 

 find the greatest development of the whirlstorm, namely, the 

 typhoon and the hurricane. 



Since the circular action of these storms was demonstrated by 

 Redfield, the interests of navigation, as well as the requnements 

 of science, have caused great attention to be paid to the subject. 

 The tracks of many of the meteors have been defined, and minute 

 directions laid down for the guidance of navigators, so that they 

 may avoid the centre or vortex of the storm. 



Yet though many opinions have been put forward to account 

 for their origin, so unsatisfactory are they considered for the 

 solution of all the phfenomena accompanying those meteors, that 

 many writers on the subject concur with Colonel Reid, that 

 " on the cause of storms, in the present state of our knowledge, 

 it is best to be silent." 



\^'hen, however, we apply the theory I have exemplified in 

 the Australian eddies, the solution of the characteristics of the 

 whirlstorm is complete and simple. As, on the land, whirlwinds 

 and eddies are most numerous whei*e the sun exerts most power 

 and the atmosphere is least agitated by winds, so over the ocean 

 we find the regions of the cyclones existing under similar condi- 

 tions. It is within a few degrees on either side of the equator that 

 the cyclones originate and are most violent. The hurricane season 

 in the northern hemisphere extends over the months of July, 

 August, September, and October; and in the southern hemi- 

 sphere, over December, Januaiy, February, and March ; and we 

 find the hurricane ti-acks to be over areas of the ocean shut off by 

 the interference of land from the continual action of the trade- 

 winds and their equalizing influence. The cyclone region of the 



