METEOROLOGY. 537 



the Baltic amounted to from 4 to 10 feet above the mean sea level, and 

 as there was a corresponding depression at the north end of the sea the 

 elevation above the simultaneous level of water on the coast of Finland 

 amounted to from 6 to 14 Dauish feet ; almost the same difference re- 

 sults from comparison with the sea level at stations on the Skagerrack. 

 (Z. 0. G. M., xvn, p. 78.) 



Dr. Hann has revived the discussion of the origin of the Fohn wind 

 by an analysis of seventeen years at Bludenz, where the Fohn comes 

 from the southeast, from the valley of the Upper 111. This valley at its 

 southeast end is bounded by the mountains covered by heavy glaciers, 

 the lowest part beiug 2,000 m. above Bludenz. On examining the cases 

 when the relative humidity is under 35 per cent., Hann finds the tempera- 

 tures are invariably far above the normal and the pressure somewhat 

 below the average; two thirds of these days occur in autumn and winter. 

 A special detailed examination was made of thirty-seven Fohn days on 

 which relative humidity was as low as from G to 20 per cent. On these 

 days the temperature was much higher and the humidity much lower at 

 Bludenz than at neighboring stations in open country to the north and 

 south, as, for instance, at Stuttgart and Milan. The barometric gradient, 

 as deduced from the general observations of the Swiss stations, show that 

 the stormy upper winds blowing over and down the mountain side are not 

 always necessary in order to produce Fohn winds in the valley; in fact, 

 the latter comes not from a distance, but is due to the air lying above 

 the summits gradually settling in valleys beneath, without having at 

 any time risen up the opposite mountain ridge. Its temperature is due 

 both to the normal warmth of the upper strata of air and the rapid 

 increase of temperature due to the compression of the sinking air. 

 (Z. O. G. M., xvn, p. 461.) 



Dr. W. Koppen presents some views concerning the rapid fluctuations 

 of temperature observed at elevated stations during anti-cyclones, 

 suggested by observations in Switzerland and Bavaria. The most 

 remarkable illustration of this variability is shown by observations 

 by Trogne, December 5-7, 1869, when from hour to hour the tempera- 

 ture and relative humidity went through rapid variations from — 7.0 

 O, and 100 per cent, to -f 10.2 C. and 30 per cent. In explanation ot 

 these Koppen allows that the insolation and the dynamic warming due 

 to compression play a part, but that the more important feature is the 

 existence of temporary horizontal gradients, producing currents and 

 mixtures of warm air with the cold air from the low-lying plains, where 

 nocturnal radiation has its greatest effect. (Z. O. G. M., xvn, p. 468.) 



VIII. — BAROMETRIC PRESSURE. 



Prof. H. Wild, in a memoir on the relation between monthly and 

 annual isobars and isabnormals of temperature, finds that these lines 

 run parallel to each other, the latter lying to the south and east of the 

 former, so that southeast of a low barometer there is always a maxi- 



