DISTRIBUTION OF RAINFALL. 275 



surface of the earth, and the rain is, as one may say, mechanically 

 pressed out of the clouds. For these reasons, it rains more on the 

 headlands than on the exposed slopes ; but in the deep fiords of 

 Norway, a pluvial rain, sharply arrested by a wall of rock, deposits 

 immediately a maximum of rain, 



" There falls annually at Bergen, 2 metres (80 inches) of rain ; at 

 Bourdeaux, only 719 millimetres (29 inches) ; at Nantes, 1 m^tre (40 

 inches); at Cherbourg, 830 millimetres (33 inches). 



" On the coast-land of the Mediterranean, the rain-producing wind 

 blows from the east, or the south-east, in a vertical direction to the 

 wall of the Cevennes, upon which descend violent showers. There 

 falls annually at Marseilles, 512 millimetres (20| inches); at Tou- 

 lon, 505 (20 inches) ; at Nismes, 640 (26 inches) ; at Montpelier, 

 770 (31 inches) ; at Viviers, at the foot of the mountains, 900 (36 

 inches); at Joyeuse, at the bottom of a valley, 1-300 millimetres 

 (52 inches). 



" The region of the Jui'a gives as characteristic of the rainfall the 

 following figures: Lyons, 776 millimetres; Magon, 876; Bourg, 

 l"* 172; Syam, in the gorge, l"* 630. 



" Some writers have erred in thinking that they may conclude, 

 from such and similar facts, that the quantity of the rainfall in a 

 place increases with the altitude of the place. Formulated thus, the 

 law is not correct ; and the phenomenon cannot be explained satis- 

 factorily. The phenomenon is mechanical as well as physical, and is 

 more intelligible when formulated thus: The pluvial ralnfallis greater 

 in proportiot), as the atmospheric current arrested hy an obstacle is com- 

 pelled to rise more rapidly. It is not then the altitude of a place 

 which is of most importance, it is the incidence with which the rain- 

 yielding wind strikes the slope which opposes it ; but the law regu- 

 lating this incidence it is not easy to determine. 



" From what has been stated it comes to pass that in order satis- 

 torily to compare two rain-gauges it is necessary to take into account 

 their absolute elevation, and along with this the slope and configura- 

 tion of the mountain sides which support them. The following table, 

 in which are brought together several localities situated in the gorges 

 of the Jura, show that the altitude is not the dominating element — 

 for the maximum of rainfall is far from corresponding with the 

 maximum of elevation : — * 



* L'Eveille: Eecherclies sur les inondation {annates de la Societe d^ agriculture 

 de Lyon, 1858). 



