DYNAMIC METEOROLOGY. 379 



of pressure or vice versa ;i change of pressure produces ii cliaugc iu 

 tbe motion; for example: Staudinj;' waves are produced at the surface 

 of a stream M'hich tend to per[)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 periodic 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 iu America, and 

 it doubtless obtains equally in India. 



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

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

 tered through the Philosophical Magazine, theproceedingsofthesocieties 

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

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

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

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

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

 nomena. These papers have apparently been drawn out as notes for the 

 forthcoming third volume of his mathematical aud physical papers, and 

 when collected will be recognized as completing our views on manj- 

 subjects. 



(20) Oberheck. — In 18S2 Oberbeck published iu Wiedemann's Annalen 

 a mathematical development based on the correct hydrodynamic for- 

 muUe, of the theory of horizontal atmospheric currents. 



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

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

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

 the proceedings of the secoud 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 i)roblems of the mathematical theory of the 

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

 immed i)henomeua. The recently published investigations of Guldberg 

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

 187G and 1S8U), are to be considered as a specially successful attempt 

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

 geograj)hers to know the most important 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 diflerences of j)ressure at the surface of the earth as observed 

 Mith 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. 



