B. TERRESTRIAL PHYSICS AND METEOROLOGY. 115 



that many documents relating to this storm still remain in 

 the hands of Messrs. Buys Ballot and Scott, who are also occu- 

 pied in the same study. His memoir is accompanied with a 

 map showing the force of the wind and the barometric press- 

 ure at every hour during the day on which the storm oc- 

 curred. The maximum violence of the wind was attained, 

 as is usual in Europe, a few minutes before the minimum 

 pressure occurred, when the direction of the wind was from 

 west-southwest. Bulletin Acad. Hoy. des Sciences, Bruxelles^ 

 2d Series, XLI., April, 1876. 



BAROMETRIC PRESSURE DURING WINDS. 



Montigny communicates to the Academy of Sciences of 

 Beliiium an investigation into the law of diminution of 

 pressure in the atmospheric strata when the state of equi- 

 librium is disturbed, especially under the influence of storms. 

 His remarks are based principally upon observations made 

 by him some years ago in order to determine the influence 

 of winds upon barometric altitudes. Having distributed his 

 observations into four classes according as they were made 

 during the periods of high or low, rising or falling barome- 

 ter, he draws the following results : First. Barometric alti- 

 tudes measured under the influence of easterly winds are 

 generally less than the true altitudes, and correspond very 

 frequently to epochs of high barometer, and rarely to epochs 

 of low barometer. Second. The altitudes under the influence 

 of east winds are least when the wind is exactly east. 

 Tliird. The altitudes calculated when west winds blow are 

 generally superior to the true altitudes, and have most fre- 

 quently been measured under the influence of storm-winds. 

 When, however, the pressures are increasing, the west winds 

 sometimes give especially low altitudes. Fourth. The num- 

 ber of storms with westerly winds is a maximum when the 

 wind is directly west; to which point also correspond the 

 greatest altitudes as computed by barometric observations. 

 Now the theoretical laws, according to which altitudes are 

 computed barometrically, are rigorously true only when the 

 air is calm. We should then conclude that under the influ- 

 ence of storms the diminution of pressure in the layers of 

 air is more rapid as we ascend vertically than when the air 

 is calm ; and, again, that this diminution is more rapid when 



