272 RELATION OF FORESTS TO THE 



observations collected and publisbed by M. Belgrand* in regard to 

 a wind-wave which passed over Europe towards the end of September, 

 1866. 



This wave originated in America, on a line which extends from 

 Buenos- Ayres to the North Pole ; it traversed the Atlantic, and reached 

 England on the 20th September, and France, Belgium, and Holland 

 on the 21st. On the 22nd, it reigned at the same time over Nancy, 

 and over Paris. On the 23rd, it raged over the sources of the Seine, 

 and of the Loire, and extended to the Garonne. On the 24:th, it 

 passed over Lyons ; its fury broke upon the St Bernard, from the 

 24th to the 26th; and from the 23rd to the 24th, upon the 

 Simplon. 



On all the elevated places it poured out a quantity of rain equal to 

 about a fifth of the average annual rainfall. On the contrary the 

 low-lying plains were almost everywhere spared ; England and Nor- 

 mandy did not receive a twentieth of the annual rainfall. Shielded 

 by the mountainous backbone of France, which stretches obliquely 

 from the Vosges to the Pyrenees, and as a watershed divides the 

 water between the ocean and the Mediterranean, Carcassonne, Mont- 

 pelier, Grenoble, Lyons, Bourg, and Bezangon did not receive any 

 extraordinary rainfall ; it did not rain at all at Strasburg, at Dresden, 

 at Munich, at Breslau — nor did it in Austria or in Italy. In Swit- 

 zerland, and even in Savoy the rain was not great, while Mont Blanc, 

 the Simplon, and the St Bernard received only 17 per cent, of the 

 annual rainfall. 



There is much that is interesting in the study of the atmospheric 

 wave, sweeping along 1700 feet above the level of the sea, with a 

 stretch of wing, extending some 1200 miles and more, skimming the 

 high lying plateaux of France, and by a flight of 200 leagues a day 

 dashing itself against the summits of the Alps ; but it is to the dis- 

 tribution of the rainfall occasioned by it with which alone we have to 

 do here. 



At the meeting of the British Association for the advancement of 

 science, held this year (1876) in Glasgow, Sir William Thomson 

 made a communication in regard to the production of the phenomenon 

 known as a " mackerel sky," which suggests an illustration of the 

 phenomenon under consideration. 



Schoolboys amuse themselves sometimes with skimming flat stones 



* Belgrand' Anuales des Fonts et Chausees. Sept. 1866. 



