SPEED OE EEYOLVING CUERENTS. 281 



west, and plunging in tlie plain of Narbonne by tlie strait wbere the 

 canal and railroads of tbe south pass, was violent enough to force off 

 the rails and partially overturn two trains which it struck cross- 

 ways, between the stations of Salces and Kivesaltes. According 

 to the engineer, Mathieu, who probably gives, it is true,, too high an 

 estimate, the pressure necessary to overturn certain carriages must 

 have been 952 lbs. per square yard of surface.* 



The masses of air which revolve not far from the central part of 

 the cyclone are the only ones which attain the considerable speed of 

 60 and 90 miles per hour. As to the movement of the whole of the 

 storm on the surface of the earth, it is naturally very slow in com- 

 parison to the circulatory movement of the aerial particles around 

 their axis. The greatest speed of translation which has been ob- 

 served is that of the hurricane in the month of August, 1853, which, 

 after having advanced at the rate of 20 miles an hour from the 

 Antilles to the bank of Newfoundland, increased gradually in speed, 

 and ended by exceeding 56 miles an hour. Most of the cyclones of 

 the Antilles move on an average from 12 to 18 miles in the same 

 space of time ; but there are some too, especially among the typhoons 

 of China, which advance so slowly that several writers have considered 

 them as revolving on the same spot. At the end of the month of 

 February, 1845, a hurricane which originated near the Mauritius 

 traversed the Indian Ocean with an average speed above 2 miles 

 per hour, while a ship, the Charles Heddles, placed at about bQ miles 

 from the axis of the storm, described immense spirals around this 



Fig. 112.— Spirals made by the vessel/' Charles Heddles." 



changing point. In five days it made five complete revolutions in the 

 midst of the sea, and though in this fantastic voyage it must at least 

 have traversed 1500 miles, nevertheless, when it was finally delivered 

 from the grasp of the cyclone, it was only at 410 miles from the 

 point of departure. The vessel had revolved like a top on the 



* Eugene Flachat, Tr aver see des Alpes. 



