§ 801-803. STORMS, HURRICANES, AND TYPHOONS. 429 



served on board ship at sea. (1.) One is diurnal rotation: it 

 alone can never work a change of direction exceeding 90° ; (2.) 

 another is the varying position or traveling motion of the place 

 of barometric depression : the change effected by it can not ex- 

 ceed 180° ; (3.) and the third is the whirling motion imparted by 

 the rush to a common centre — the whirl of water at the flood- 

 gate of the mill, the whirlwind in the street. 



801. Hence it appears that in a storm the wind may shift from 

 The effect of each, any onc of thrcc causcs, and we are not entitled to 



call it a cyclone unless the wind shift . more than 180°. If the 

 change of direction be less than 90°, the shifting may be due to 

 diurnal rotation alone ; if it be less than 180°, the shifting may, 

 and is probably, due to (1) and (2). The sailor has therefore no 

 proof to show that he has been in a cyclone unless the wind dur- 

 ing the storm changed its direction more than 180°. Cyclones, 

 there is reason to believe, are often whirlwinds in a storm. This 

 may be illustrated by referring again to our miniature whirlwinds 

 on the land; there we often see a number of them at one time 

 and about the same place ; and they often appear to skip, raging 

 here, then disappearing for a moment, then touching the ground 

 again, and pursuing the former direction. 



802. Observations have proved that this is the case on land, 

 A stonn within a storm, and obscrvatlous havc not established that this is 

 not the case at sea; observations are wanting upon this subject. 

 Tornadoes on the land often divide themselves, sending out branch- 

 es, as it were. It remains to be seen whether cvclones do not do 

 the same at sea ; and whether, in those widespread and devastat- 

 ing storms that now and then sweep over the ocean, there be only 

 one vortex or several ; and if only one, whether the whole storm 

 partake of the cyclone character. In other words, may there not 

 be a storm within a storm — that is, a cyclone traveling with the 

 storm and revolving in it ? I ask the question because the theo- 

 ry does not satisfy all the facts observed. 



803. The celebrated Black Sea storm of 1854, which did so 

 The Black Sea storm ^luch damage to the allied fleet, is still maintained 

 ° "^ ' by some to be a true cyclone ; and by the observa- 

 tions of some of the vessels a cyclone may be made out. But if 

 we take the observations of all of them, and discuss them upon 

 the supposition that the whole storm was a cyclone, it will puzzle 



