112 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 







slopes most intensely. These are the slopes that are almost 

 every where destitute of trees, although they receive the 

 greatest rainfall and the most fog. The winds act in two 

 ways: first by their drying power, and second by their cool- 

 ness ; perhaps also by their influence in spreading fires dur- 

 ing the dry seasons. The forests are chiefly most extensive 

 on the northeastern mountain slopes. Proceedings of the 

 California Academy of Science^ V., 286. 



PEKIODICITY OF HUKEICANES. 



In the March and April numbers of the Revue 3Iaritime 

 et Coloniale, Vice-Admiral Fleurcote de Langle examines 

 the question of the periodicity of hurricanes throughout the 

 globe ; having reference especially to the influence of the 

 sun and of the moon. He concludes that for a given lati- 

 tude of the earth's surface we can, by knowing the positions 

 of the sun and the moon, compute the probability of experi- 

 encing a hurricane on any given day. For this purpose he 

 gives tables based upon a complete analysis of recorded 

 hurricanes, the reliability and usefulness of which is, how- 

 ever, somewhat problematic. Revue Maritime et Coloniale, 

 1876,129. 



CLOUDS AND WINDS AS OBSERVED FROM BALLOONS. 



In some notes on the formation of clouds, Villeneuve 

 states that when the sky is covered with nimbus or cumu- 

 lus, one always meets on ascending in a balloon with Avinds 

 moving either in a contrary direction, or crossing each other 

 under variable angles,or if very nearly in the same direction, 

 then with very difierent velocities ; and these winds have 

 very difierent temperatures. Second, when the sky is with- 

 out clouds, or we see only cirrus, we find at all altitudes 

 winds moving in the same direction, or, exceptionally, two 

 winds in different directions, but having sensibly the same 

 temperature. In explaining these phenomena, he lays down 

 the rule that the thickness and the form of clouds are func- 

 tions of three causes : first, the difference between the tem- 

 peratures of two superposed currents of air ; second, the 

 relative velocity of one current over the other ; third, the 

 deo^ree of humidity; and it can happen but rarely, he states, 

 that two currents moving in different directions do not pro- 



