472 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



It remains to be sliown whether the irregular atmospheric currents 

 and storms which produce in each month the extreme variations of the 

 barometer increase in intensity with the latitude ; whether this intensity 

 doubles as we pass from equatorial regions to temperate zones and 

 trebles when we pass to the polar regions. 



A precise verification cannot be made at present. We possess no 

 direct observations upon the mean velocity of the atmospheric currents 

 in different latitudes; but we can assert that the ratios of the intensities 

 to which our theory leads us do not differ very much from the reality. It 

 is well established that, as the regular winds diminish, the frequency and 

 the violence of the irregular currents and of the tempests increase in pro- 

 portion as we depart from the equator. The reason would seem to be 

 that indicated by Kiimtz.* The first cause of every current in our atmos- 

 phere is an irregularity of temperature. Now, in proportion as we 

 j)roceed from the pole toward the equator, the thermometric variation 

 for any change in latitude becomes more rapid; the distribution of tem- 

 perature upon the same parallel becomes more irregular. In general, 

 we think it certain that our formula suffices to explain the enormous 

 variation of the monthly barometric oscillation as one passes from the 

 equatorial to the iJolar regions. 



(8) Calculation of the Velocity of the Wind from the Variations of 



Barometric Pressure. 



The relation that we have found between the velocity of the air in 

 any atmospheric current and the variation of barometric pressure in a 

 direction transverse thereto should permit us, inversely, to calculate the 

 velocity of the air when we know the law of the variation of the 

 pressures. The synoptic charts, by giving us for every day the law of 

 the distribution of pressure over a certain region of the earth, enable us 

 to deduce the mean velocity that should be presented by the atmospheric 

 currents prevailing over this region. To this end it sutfices to resolve 

 the equation 



Ap = — 2PV^smXJr 

 9 



with reference to the velocity V considered as an unknown quantity : 

 thus we obtain 



7 _ -O^P 



2p Q> sm?.Av ' 



In the synoptic charts the isobars are traced for pressures differing 

 by five millimeters. For the value of the arbitrary distance Ar, I take 

 the distance of the two isobars which include the point under considera- 

 tion. The corresponding value of J?? would be equivalent to a height 

 of 5 millimeters of mercury, and we consequently have 

 #_ O^.OOS X 13.596 



^ 0.001293 XrrlW:X '^ 



0.7GU l-{- at 



* Kiimtz, Meteorologie, p. 281. 



