B. TERRESTRIAL PHYSICS AND METEOROLOGY. G5 



servatory in Tiflis. Abich considers, especially, the meteor- 

 ological influences of forest growth, and of altitude above 

 the sea-level, and states very strongly his opinion that only 

 a complete misunderstanding of the facts related by him, and 

 of the general conclusions of other students, especially those 

 of Miihrv, could lead one to believe that the influence of the 

 forests can be insignificant upon climatology, and especially 

 upon the cultivation of the soil ; the preservation of forests 

 must therefore be considered as an object worthy of most 

 serious consideration and earnest national enterprise. With- 

 in the foliage the moisture of the atmosphere is condensed ; 

 and in consequence of a complicated process, it results that, 

 from the upper surface of the foliage of a forest, cold air flows 

 down. This air slightly raises its temperature, and preserves 

 the earth, in the interior of the forest, at a temperature sev- 

 eral decrees higher on the average than that which is not 

 protected. The forest, in fact, operates in a manner very 

 similar to the ocean or a large lake. As the sea wind blows 

 upon land during the daytime, so during the daytime the 

 cold air of the forest blows out toward the open fields. As 

 the land wind at night flows toward the ocean, so in the 

 evening the cold air in the forest, receiving the warmth of 

 the warm earth, rises up, while the cool air from the exterior 

 region flows in to take its place. This daily vertical com- 

 pensating circulation has an intensity proportional to the ex- 

 tent of the forest and the barrenness of the soil that is not 

 protected. In regard to the formation of hail, he concludes 

 that it is determined by the conditions existing in the upper 

 regions of the air; but the direction of the movement of the 

 hail-storm, and its variable intensity, from point to point, are 

 principally determined by local influences, and especially the 

 vertical currents of the atmosphere that depend for their ex- 

 istence upon the presence of forests, heated plains, rivers, etc. 

 3/oritz, 3Iaterialsfor the Climatology of the Caucasus, vol. i. 



OX THE PERIODICITY OF CLIMATES OX THE EARTH. 



The question whether there are any other regular periods 

 in meteorology than the daily and annual has, as is well 

 known, attracted great attention of late years in connection 

 with the supposed discovery of an eleven-year period coin- 

 ciding with the increase and diminution of the solar spots. 



