14 ^ THE LAW OF STORMS. 



3. A dirty green appearance of the ocean ; on some 

 occasions its assuming a muddy or brown color, on others 

 its being remarkably clear, its temperature increas- 

 ing, and its swellings stronger than at other times,^— 

 are all indications of the proximity of a cyclone. 



The area over which these rotary storms have been 

 known to expand, varies from 30 to 40 to 1,000 miles; 

 but while the diameter, so long as the storm is within 

 the tropics, expands but very gradually, it suddenly in- 

 creases in a remarkable manner after recurving. The 

 rate at which they travel on their onward course also 

 varies greatly, not only in different parts of the globe, 

 but even in the same locality, and at the same season. 

 Generally, however, the rapidity with which the vortex 

 of the hurricane progresses is greater as the storm re- 

 curves on reaching the outer edge of the trade winds. 

 Thus, the hurricane of August, 1853, traversed 6,276 

 English miles in about twelve days, with a mean pro- 

 gressive velocity of twenty-six miles per hour ; but after 

 it arrived at the Banks of Newfoundland this velocity 

 was increased to about fifty miles per hour. 



Within the area of the cyclone the moving body of 

 air frequently attains a rotatory velocity of from seventy 

 to one hundred miles an hour. 



