r^YNAMIC METEOROLOGY. 379 



of pressure or rice versa ;i clianj^e of pressure produces a cliiiuge in 

 the motiou ; for example: Staudiug waves are produced at the surface 

 of a stream which tend to i)eri)etuate themselves; the atmosphere is 

 thrown into a system of undulations by mountain ridges, plateaus, and 

 continents (which undulations may also be horizontal deviations on a 

 grand scale) and into i)eriodi(; recurrences due to their own inertia and 

 therefore as Eliot says, tending to reproduce themselves until broken 

 up by outside disturbances. This is the explanation of the special sea- 

 sons of droughts, storms, and rains that we experience in America, aud 

 it doubtless obtains e<iually in India. 



(19) Sir William Thomson. — Thompson has published a series of papers 

 sparkling with his customary brilliancy on Huid motions ; these are scat- 

 tered through thePhilosophical Magazine, theproceedingsofthesocieties 

 at London, Edinburgh, and Glasgow, and the reports of the British As- 

 sociation. These pajjcrs will cover theoretical questions as to the sta- 

 bility of tluid motions, the formation of standing waves, the discontin- 

 uous space in the rear of an obstacle, the laminar flow of liquids, the 

 turbulent flow of water, and other matters bearing on atmospheric phe- 

 nomena. These i)ai)ers have apparently been drawu out as notes for the 

 forthcoming third volume of his mathematical and physical i)apers, and 

 when collected will be recognized as completing our views on many 

 subjects. 



(20) Oherheek. — In 1882 Oberbeck published in Wiedemann's Annalen 

 a mathematical develoi)ment based on the correct hydrodyuamic for- 

 muhe, of the theory of horizontal atmospheric currents. 



A full translation of this important memoir will be included in the 

 series of papers formerly referred to; but the following i)opular state- 

 ment of his results is given here as published by Oberbeck himself in 

 the i)roceedings of the second German Geographical Congress: 



Starting from the generally known results of recent meteorological 

 observations in so far as these relate to the distribution of pressure 

 and the direction and force of the wind, the author explains that one 

 of the most important problems of the mathematical theory of the 

 motion of fluids is to explain quantitatively the connection of the above- 

 named phenomena. The recently published investigations of Guldberg 

 and Mohn (Etudes sur les mouvements de I'atmosphere, Christiania, 

 1870 and 1880), are to be considered as a specially successful attempt 

 in this direction. It must be of interest also for the larger number of 

 geograjihers to know the most imi)ortant results to which the Norwe- 

 gian scientists have attained. 



In order to understand the horizontal movements of the atmosphere 

 it is important for a moment to consider their causes. As such we con- 

 sider the differences of pressure at the surface of the earth as observed 

 with the barometer. But whence do these arise? This question has 

 been answered a long time since. It is heat which is to be considered 

 as the prime cause of the disturbance of equilibrium in the atmosphere. 



