SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 435 



mile], then must the value given by this formula be multiplied by 12.5 

 (or J^). 



lu the night of January 26-27, 1874, we experienced in Vienna the 

 most violent storm (from the W:N^W.) since the establishment of the 

 new anemometer. The maximum velocity of the wind attained 31 

 meters per second (see this Journal, vol. ix, p. 62). The mean velocity 

 between 7 a. m. and 8 a. m. was 27.5 meters. The synoptic charts of 

 Captain Hoffmeyer show that on this morning an area of low pressure 

 (720 millimeters) existed in the neighborhood of St. Petersburg, and that 

 the gradient toward this point was, in the neighborhood of Vienna, 0.22 

 millimeter per German mile. 



If we put (p = 48°, v = 27.5, and r = 1630 kilometers, or about the dis- 

 tance of Vienna from St. Petersburg, then we find from the preceding 

 formula : 



Ji> resulting from the earth's rotation = 0.214 

 JB resulting from the centrifugal force = 0.033 

 Therefore the whole /iB = 0.25 



We see clearly from this that even the imperfect theory affords a very 

 approximate value for the barometric differences. It further follows that 

 the influence of centrifugal force may be neglected in the storms of our 

 latitude, which generally extend over a very great extent of surface, and 

 in which the greatest velocity of the wind does not commonly occur in 

 the neighborhood of the storm-center (or rather of the lowest barome- 

 tric pressure). For comparison, I will add that the greatest gradients 

 known to me directly from our telegraphic weather-reports are the fol- 

 lowing: 



1869, November 14, 7 a. m.— Wiud WNW., force 10 at Vienna. Gra- 

 dients : from Vienna to Cracow, 0.22 ; Vienna to Ischl, 0.28 millimeter 

 per German mile. 



1869, December 2, 7 a. m. — Bora of hurricane force in the Gulf of 

 Trieste and in the Adriatic : The gradient from Klagenfurt to Pola was 

 0.31 millimeter. 



We will now consider a tropical whirlwind, and choose that which 

 devastated the island of St. Thomas on the 21st August, 1871. The 

 observations show that at distances of about 57 and 111 English miles 

 from the central point of the whirlwind the pressures were respectively 

 10 and 17 millimeters higher than in the central calm space, whose radius 

 was 3.6 English miles. This gives gradients of 0.86 millimeter and 0.60 

 millimeter for one German mile. If we substitute in the formula the 

 numerical values y = 28°, v = 30, r = 57 English miles = 91.7 kilome- 

 ters, we find 



AB as the effect of the earth's rotation = 0.10 



AB as the effect of the centrifugal force = 0.71 



AB the total of both influences = 0.81 



Therefore, a wind- velocity of only 30 meters suffices to explain the 

 observed extraordinary difference of pressure, AB = 0.73, in a distance 



