THE LAW OF STORMS DEVELOPED. 



389 



Such a meteor has been shown to resemble an eddy moving in the cur- 

 rent of a rapid river. The latter may be large or small, while it does 

 not determine, but is determined hy, the course of the on-flowing stream. 

 It is true the centre of an eddy or water-hollow may soon be tilled up 

 and the whirl disappear; but it is because the depression is not main- 

 tained. If the depression could be maintained, it is easy to see that 

 the eddy would eontinue, and pursue its way, as long as the current 

 in which it is embodied continues to flow: it mischt be through the 

 length of an Amazon or a Mississippi River. In the case of a cyclonic 

 eddy or whirl, we know the atmospheric depression is maintained as 

 long as the centre moves in a region sufficiently supplied with aqueous 

 vapor to feed it. It is a physical impossibility, as has been often 

 shown, that any storm, however vast or however violent, can prolong 

 its advance or sustain its fury over a dry and desiccated surface. The 

 most extended typhoons of the East, upon entering the dry and rainless 

 continental regions, dwindle into the well-known and diminutive dust- 

 whirlwind, such as Sir S. W. Baker describes as witnessed in Nubia, and 

 as here illustrated. The Sahara is a more formidable barrier to the 



Fig. 2. 





THE DUST-WHIRLWIND. 



passage ol a storm than the majestic mountain-wall of the Alps, and 

 the simoom is, notwithstanding the stories of travellers and the 

 legend of swallowing up of the army of Cambyses on the African des- 

 ert, a wasted and worn-out cyclone. In his " Desert World," Mangin, 

 compiling the more accurate observations of the phenomenon says : " It 

 never prevails over any considerable area, and beyond its limits the 

 atmosphere remains serene and calm ; the phenomenon is of brief dura- 

 tion, the atmospheric equilibrium is speedily restored ; the heavens 

 recover their serenity ; the atmosphere grows clear, and the sand-col- 

 umns, falling in upon themselves, form a number of little hills or cones, 



