464 J^HOKT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



The values of the pressure z given in the lowest line are those which, 

 according to d'Etroyat's observations, belong to the corresponding 

 values of x = 0.1 H, &c. But, according to equation (3), we can deter- 



mine the constant — by means of each pair of X and z. We have for 

 this purpose the ten numerical equations 



F2_10.()nim _i7.o _21.5 „ 



and as the mean of these ten values we iind 



y2 



— = 13.7"^°" of mercury, according to d'Etroyat; 



similarly, 



— = 13.2"''" of mercurv, according to Taylor. 

 (J 



By using these constants, we can now, for each value of a; = 0.1 H, &c., 

 compute the corresponding value of 0. This computation, executed for 

 both the series of observations by d'Etroyat and by Taylor, gives the 

 following result: 



^=0.1 0.2 0.3 0.4 0.5 O.G 0.7 0.8 0.9 1.0 



D'Etroyat. 



;^ observed .. 10.0 17.0 21.5 24.5 27.0 28.5 29.5 30.5 31.0 31.7 

 5; computed. 11.9 17.9 21.7 24.4 26.5 28.2 29.1 30.1 30.8 31.2 



The agreement is therefore almost perfect. D'Etroyat's observations 

 give for — the value 13.7 millimeters of mercury, or 460 feet of air j 



Taylor's observations give 440 feet of air. From these It follows that 

 y = 120 feet or 39 meters and 117 feet or 38 meters. Since the velocity 

 of the forward progress of the whirlwind was 12 miles, or 20 feet per 

 second, therefore must the greatest velocity of the wind on the right 

 side of the whirl, where the rotatory and the progressive movements take 

 place in the same direction, be considered to be 140 feet or 45.5 meters; 

 but on the lett side, where the inverse is the case, it becomes 100 feet or 

 32.5 meters. For a; = U the equation (1) gives in our case i? = 68 feet as 

 the velocity of rotation at the outer limit of the whirl. This would give 

 a velocity of S^ feet on the right and 48 feet on the left-hand side. 

 Therefore between these limits ranged the velocity of the wind within 

 the cyclone of the 21st August, 1871. 



