402 TRANSACTIONS OP THE 



REVOLVING STORMS. 



The following article on revolving storms, etc., was published in the 

 San Francisco Daily " Call," April 2, 1889, the article being furnished that 

 paper by Lieutenant H. P. Mcintosh, of the Hydrographic Office, in the 

 Merchants' Exchange, San Francisco, with a few notes added by the Lieu- 

 tenant. The article is intensely interesting, and well worthy of careful 

 perusal and close study: 



Revolving Storms — How Do They Occur, and What Governs Their 

 Movements — Peculiarities of Samoa — Illustration of How the Wind 

 Revolves Toward the Center of Low Barometer. — The recent meteor- 

 ological phenomenon at Samoa has opened a field of inquiry with reference 

 to hurricanes, tornadoes, typhoons, or by whatever name they may be classi- 

 fied, that will probably result in a more careful study of the causes, tracks, 

 and influences than ever before. All information at- this time is obscure, 

 and, in a great degree, speculative. It has been established, however, that 

 all are in a greater or less degree cyclonic, and that while they may be mov- 

 ing ahead at the rate of from eighteen to twenty miles an hour, the current 

 within the air whirlpool is of terrific force. The nearer the center of the 

 vortex, the greater the velocity. 



AVERAGE VELOCITY. 



The average velocity of the cyclone varies greatly, not only in different 

 parts of the world, but in the same localities, and at the same season of the 

 year. The size of a cyclone does not afford any rule whereby to estimate 

 its rate of traveling, as both large and small ones are known to move with 

 great rapidity, or at moderate or slow rates, without, apparently, any sort of 

 law. It has been conjectured that the vortex below was carried forward by 

 currents of wind above; but it is objected to this that the upper strata of 

 clouds are often seen, through breaks in a storm, to move across or against 

 the track of the cyclone, which itself has a track against the prevailing 

 winds, as in the Atlantic hurricanes, moving to the east against the trade 

 winds, the track of one having been observed for a distance of three thou- 

 sand miles; or oblique to them, as the hurricanes of the Southern Indian 

 Ocean, moving to the westsouthwest across the southeast trade. 



These facts leave observers completely in the dark as to what causes 

 their progressive motion, and also as to what causes their violent gyrations. 

 This state of feeling is intensified by the fact that, like sandstorms or dust 

 whirlpools, they will sometimes remain stationary for hours, and even for 

 a day or more, moving at a rate of one fifth to two miles an hour, and then 

 start off on a track upon which their size and velocity gradually increase. 

 Usually they diminish in velocity in passing over land, and particularly if 

 it is high land. 



According to Redfield the West Indian and North American cyclones 

 range from nine and five tenths miles an hour to forty-three miles. This 

 would make a mean rate of about twenty-six miles. In the Southern 

 Indian Ocean Thorn estimates the rate of traveling to be from nine and 

 ten minutes to a little more than two miles an hour. Colonel Reid, in his 

 chart of the cyclone of 1809, lays down from seven to twelve and one half 



