B. TERRESTRIAL PHYSICS AND METEOROLOGY. 113 



duce clouds at their surface of contact. This occurs, how- 

 ever, only when they are sensibly at the same temperature. 

 He has observed this fact in north winds blowing above 

 east winds ; but never in the case of south winds blow- 

 ing above north winds. Some aeronauts have observed 

 four currents superposed and blowing in diflerent direc- 

 tions. This condition is extremely favorable to the forma- 

 tion of rain. According to Villeneuve, if w^e could know 

 the temperature of the winds which are superposed above 

 our heads and their hygrometric state, we should be able to 

 announce with certainty whether rain or cloudiness would 

 ensue. L^Aeronaute, November^ 1875, 321. 



HIPP'S ANEMOMETEE. 



A description of the anemometer recently invented by 

 Mr. Hipp is given by him in the tenth volume of the Bulle- 

 tin of the Scientific Society of Neuchatel. The object of 

 this anemometer is to register at any distance whatever the 

 velocity or the total movement of the air. It permits one 

 to determine at any minute the velocity of the wind. The 

 wind acts upon the ordinary Robinson atmospheric cups, 

 and these can be placed at any distance from the registering 

 apparatus, communicating with it by electric telegraph. 

 Clock-work communicates a movement to the long band of 

 paper destined to receive the register. Velocities as high 

 as fifty miles an hour are registered on this band, but the 

 apparatus can easily be enlarged to record the highest ve- 

 locities that occur in hurricanes. Bulletin Soc. des Sciences 

 Naturelles^ JSfeuclidtel^ X., 189. 



dufoue's hygeometeic studies. 



Dufour has presented to the Society Yaudoise a second 

 memoir on hygrometric diff^usion, in continuation of that 

 published in 1874. The following is a general summary of 

 his conclusions : 



When a partition of porous earth separates two masses of 

 air in difterent hygrometric states, there are produced two 

 opposite and unequal currents of diffusion traversing the 

 partition. The greater current flows from the dry to the 

 humid air. The difference of tlie two currents depends 

 principally upon the difference in tension of the vapor on the 



