300 THE NATURALIST IN NICARAGUA. [Cli. XVI. 



dry and bare, with great cracks in the black soil. , The 

 grass had not sprung up ; not a breath of air was stir- 

 ring; and the heated air quivered over the parched 

 ground, forming in the distance an imperfect mirage. 



Directly overhead the noonday sun hung in the hot, 

 hazy sky. As we moodily toiled over the plain, my 

 attention was arrested by a dust whirlwind that suddenly 

 sprung up about fifty yards to our left. The few dry 

 leaves on the ground began to whirl round and round, 

 and to ascend ; and in a minute a spiral column was 

 formed, reaching, perhaps, to the height of fifty feet, con- 

 sisting of dust and dry dead leaves, all whirling round 

 with the greatest rapidity. The column was only a few 

 yards in diameter ; and it moved slowly along, nearly 

 parallel with our course, but only lasting a few minutes ; 

 so that before I could point it out to Yelasquez, who had 

 ridden on ahead, it had dissolved away. I had been 

 very familiar with these air eddies in Australia, and 

 had hoped to carry on some investigations concerning 

 them, begun there, in Central America ; but, though 

 common on the plains of Mexico and of South America, 

 this was the only one I witnessed in Central America. 



The interest with which I regarded these miniature 

 storms was due to the assistance that their study was 

 likely to give in the discussion of the cause of all 

 circular movements of the atmosphere, including the 

 dreaded typhoon and cyclone. All the chief meteoro- 

 logists who have discussed this difficult question have ap- 

 proached it from the side of the larger hurricanes. There 

 is a complete gradation from the little dust eddies up 

 through larger whirlwinds and tornados to the awful 

 typhoons and cyclones of China and the "West Indies ; 



