462 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



siderably greater than the quantity of air which, at each separate degree 

 of latitude, returns toward the equator. Hence it evidently follows that 

 the atmosphere in its entirety, with the excess of pressure which takes 

 place from west toward east, must move from west to east around the 

 firm surface of the earth ; and hence, again, it follows that Dove's law 

 of revolution for the wind must be a natural law. 



I shall, for the present, not consider further the conclusions which may 

 probably present themselves, and that may be deduced with regard to 

 the phenomena of wind and weather. It seems, however, to be pretty 

 clear that these deductions may be more important than anything that 

 we have hitherto known on the subject we have been considering. 



J. 



ON THE WHIRLWIND AT ST. THOMAS ON THE 21ST OF 



AUGUST, 1871. 



[We here append a trauslation of Hann's extracts (Zeitscbrift, s, p. 141), from a sec- 

 ond memoir by Colding, entitled "On the Whirlwind at St. Thomas on the 21st of 

 August, 1871," and which is published at page 10 of the volume for 1871 of the "Pro- 

 ceedings of the Danish Academy."] 



On the 21st of August, 1871,* a whirlwind passed over the West 

 India Islands in the direction from ESE to WNW. The reports show 

 the average velocity of its progress to have been 12 English miles per 

 hour. The center of the hurricane passed directly over the city of 

 St. Thomas about 5 o'clock p. m. During the whole day before the 

 outbreak of the hurricane the wind blew from NNE to ENE. The 

 barometer before noon stood at 7G5.5 millimeters, and fell about 1.5 

 millimeters from morning to evening. The pressure continued falling 

 throughout the night, and the wind increased in force. About 4 a. m. 

 of the 21st, the barometer stood at 763 millimeters, and remained sta- 

 tionary at this point until 9 a. m. The wind blew in gusts, with squalls 

 from the east and northeast, and heavy rain fell. At 12.30 p. m., the 

 barometer stood at 760; the wind was more northerly, and blew in fear- 

 ful gusts. At 2.30 p. m., the pressure was 755.5 millimeters; the wind 

 veered to northwest at 3.30 p. m., and blew with terrific power. The 

 heaviest winds, which caused great damage, occurred about 4.30 and 5 

 p. m., and came from the northwest. At 5 p. m., it suddenly became 

 still, as the center of the hurricane drew near. The city was enveloped 

 in a thick, dark fog, and the air was unnaturally quiet. During this 

 calm, the pressure reached its lowest point, 727.5 millimeters. After an 

 interval of 35 minutes, the hurricane began anew with heavy squalls 



* The subsequent path and other phenomena of this hurricane, which passed over 

 Panta Rassa on the 23d, were successfully predicted from day to day in advance by 

 the present translator in the tri-daily weather probabilities of August, 1871, as pub- 

 lished by the Army Signal Office. — C. A. 



