io THE AIR 



may be manoeuvred out of the track of the centre 

 after the approach of the storm has been signalled on 

 board by the fall of the barometer, the shift of the wind, 

 and the characteristic cloud formation. They are 

 accompanied by wind of terrific force, falling to a calm 

 in the centre of lowest pressure (" the eye of the storm/' 

 where a glimpse of blue sky breaks the pall of cloud), 

 and rising again as the barometer leaps up, to even 

 greater force than before, though from a different direc- 

 tion. Such storms in the Indian Ocean and Mozam- 

 bique Channel are called cyclones, and to describe 

 them the word was first devised ; in the West Indies 

 they are called hurricanes, and in the China Sea 

 typhoons. The rapid fall of the barometer to an 

 extremely low point, and its equally rapid rise, is the 

 most striking characteristic of such storms from the 

 meteorological point of view. A synoptic isobaric 

 chart, showing the pressure at the same moment at a 

 large number of points during such a storm, exhibits 

 a series of concentric, nearly circular isobars, the 

 lowest in the centre ; and successive charts at short 

 intervals of time show that the storm travels with 

 more or less regularity in a curved path, which, as a 

 rule, can be fairly accurately forecasted by observations 

 of the wind and the movements of the barometer. 

 These storms move from the tropics first in a polar 

 west direction, and later in a polar east direction — 

 in other words, their track is at first towards the 

 west, curving as they proceed towards the right in 

 the northern hemisphere, and towards the left in the 

 southern hemisphere. 



We know little or nothing at present of the generation 

 of these violent cyclonic storms, though from the fact 

 that the appearance and movements of cirrus, the 

 highest form of cloud, usually give the first signal of 



