Meteorological Notes

Abstract

MEAN ATMOSPHERIC PRESSURE OF EUROPE.—A great contribution to this very important subject has been made by Dr. Buys Ballot in the second volume of the “Nederlandsch Meteorologisch Jaarboek voor 1872,” which has just been published. The first 130 pages of the volume are occupied with a very careful and in certain directions exhaustive discussion of the barometric observations made at about 110 places situated in different parts of Europe from 1774 to 1874. The method of discussion is identical with that adopted by Dr. Buys Ballot in his recently published paper on the Meteorology of Holland (NATURE, vol. xvi. p. 89). This method consists in accepting as the normal mean atmospheric pressure at Greenwich, Vienna, and Palermo, the arithmetic means of the observations made at these places which embrace periods of 100, 101, and 84 years respectively. The normal values for the other stations have been determined by the process of differentiation, that is, by a comparison of the means of all the observations made at the place with the corresponding means of one or more places at the nearest available stations whose normals have been already determined, and thereafter applying the necessary correction. Thus the normals which have been arrived at in this very laborious manner are substantially the averages which would have been obtained if the observations at each of the stations had been made during precisely the same terms of years. The thirty years' averages should probably have been accepted as the best normals for Stykkisholm in Iceland, instead of correcting these averages from the Greenwich and Christiania observations, seeing that a low average barometer at Stykkisholm is frequently coincident with a high barometer at either or both of these stations, and vice versâ. The resulting differences, however, are but slight. This work of Dr. Buys Ballot, particularly when looked at with reference to future discussions, may be said to take a place at once as a classic of meteorology. The next step to be taken in this field of European meteorology is the discussion of all good barometric observations made in Europe during the meteorological lustrum ending with 1875. To the results of this discussion corrections could be applied from Du Buys Ballot's normals, which are sufficiently numerous for the purpose, and thus a graphic representation could be made of the closest possible approximation to the true mean atmospheric pressure of Europe. In this way, by disclosing the striking, and in a large measure still unrecognised, influence of large masses of land and water on the barometric pressure, much light would be thrown on the origin and history of those great atmospheric currents which, flowing or sweeping over this continent, are mainly instrumental in determining the climates of its different regions.