METEOROLOGY. 339 



6. The time of afternoon minimum varies from 3 P. M. in winter to 5 

 p. M. in summer. 



7. The morning minimum disappears or is very flat. 



8. The morning maximum occurs very earl^" — on tlie average at 8 A. 

 M.; and the evening maximum, which is more pronounced than in open 

 localities, is much delayeil — even until 1 a. m. 



With reference to the cause of the differences in diurnal periodicity 

 between valley and mountain stations, he remarks only that the princi- 

 pal cause, as long since recognized, is the expansion and contraction 

 with temperature of the stratum of air below the mountain, but that, 

 besides this, dynamic causes contribute especially to the formation of 

 the evening maximum. A further investigation will be given by him 

 when he has secured two full years of all the observations at high and 

 low stations. {Z. 0. G. M., xviri., p. 290.) 



276. [Many studies have contributed to show how slight is the diurnal 

 change of temperature of the great mass of air, and we may therefore 

 doubt whether the expansion and contraction corresponding to this 

 slight diurtial temperature change suffice as a static explanation of the 

 diurnal barometric differences at the top and bottom of a high mount- 

 ain. We are rather inclined to think this a minor factor in the expla- 

 nation of the phenomena to be studied by Pernter, and that he will 

 find that some kinetic law covers the whole ground. The broadest 

 basis for this explanation has been given in the investigations by Ferrel 

 and others, and I have for many years taught that the phenomena, after 

 allowing for a small static influence, are reducible to three dynamic 

 causes: one general for the whole earth's surface; a second, special for 

 the latitude and the continent; a third, and least important, special for 

 the locality, its altitude and its immediate surroundings, including the 

 exposure of the barometer to the influence of winds.] 



277. Andre, of Paris, has studied the diurnal variation of the barom- 

 eter at different altitudes above the sea, and confirmed the results re- 

 cently announced by Hann, Pernter, and others. He also concludes the 

 existence of a third maximum in the winter months, occurring about 

 2.30 P. M. {Z. 0. G. il/., XIX, p. 143.) 



278. Dr. E. Maurer publishes in full the results of hourly barometric 

 observations for one year — April, 1883, to March, 1884 — on the summit 

 of the Santis and the Great St. Bernard, and comj^ares these with ob- 

 servations made at other high stations in the Alps. The mean gradient 

 between the two stations is as follows : For the spring, 0.10 ; for the 

 summer, 0.22 ; autumn, 0.G9 ; winter, 1.10 millimeters. These figures 

 give a new demonstration of Hann's conclusion, that only in winter in 

 extra-tropical latitudes can great general gradients occnr in the higher 

 atmospheric strata, while in summer, with a much more uniform distri- 

 bution of temperature, warmth, and moisture, the gradient is slighter. 

 {Z. 0. G. ill., XIX, p. 513.) 



^79. Prof. B. Busin, of Eome, suggests that we may derive advantage 



