Natural History. 215 



Sometimes, in this last case, it resumes its force a little further on. 

 v. The forests attracting, but not always arresting the progress of 

 storms ; it may happen, that storms, which were proceeding at a 

 distance from each other, through the attraction of a forest are 

 made to approach, and hence are disposed to unite either before or 

 after passing over the forest. In this last case, a storm may ap- 

 pear stronger after having passed a forest, and when it goes off 

 from it, than it was before arriving there — a natural effect which 

 agrees with other observed phenomena, but which may deceive and 

 appear in contradiction to aphorism iv. (6). 



vi. A storm may follow a great river or a valley, provided, how- 

 ever, that it does not turn it considerably from the direction it 

 would otherwise take. 



(a) If this direction is nearly parallel to the river or to the 

 valley, it will coincide with it exactly. 



(6) But the approach of a forest, or rather a sharp turn in the 

 river, or in the valley, will make it abandon it. 



vii. A storm, the direction of which crosses that of a river or a 

 valley, meets no obstacle therein and no delay. 



viii. One stormy cloud attracts another not far distant, and makes 

 it deviate from its route. There is reason to believe the action is 

 reciprocal, and, consequently, that the deviation of each cloud is 

 inversely as its power, allowance being made for accessary circum- 

 stances. 



ix. One cloud attracted by a stronger one accelerates its mo- 

 tion as it approaches the principal storm. 



x. When there is an affluent cloud, which was itself occasioning 

 destruction — 



(a) It ceases its ravages occasionally when approaching the 

 principal storm — a consequence perhaps of the acceleration of its 

 progress. 



(6) But after the junction, the mischief usually increases. 



25. Peculiar Phenomena of Humidity. — In the Memoirs of the 

 Petersburg Academy, it is stated that, in the district of Gori, in 

 Russia, at the foot of the Ossetin Mountains, there is a hill, on the 

 stony surface of which, the humidity that exudes from the rock 

 in summer and in fine weather is converted into ice, of a thick- 

 ness proportionate to the heat of the sun. This ice disappears in 

 the night, or during cloudy weather so completely that the rock is 

 scarcely damp. The water obtained from the melted ice appears, 

 upon analysis, to contain only a very small quantity of lime, and 

 no other foreign matter. — N. M. Mag. xxvii. 311. 



26. Meteorology. — M. Flaugergues,who has studied very closely 

 the action of the moon upon our atmosphere, by observations carr 

 ried on during twenty years, has found constant a certain relation 

 between the number of rainy days and the phases of the moon. A 



