114 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



opposite sides of the partition. Temperature has little or no 

 eftect. Second. Hygrometric diffusion takes place through 

 plates of marble five millimeters in thickness, homogeneous 

 and compact, polished or not polished ; but it is slower in 

 this case than when traversing partitions of porous earth. 

 Diffusion is observed also through gypsum, charcoal, and 

 alabaster, beinoj slowest in the latter case. Third. When a 

 limited volume of air is inclosed in a vase, of which one side 

 is a porous partition, there is produced and maintained be- 

 tween the interior of this vase and the surrounding air a dif- 

 ference of pressure, if the hygrometric conditions are differ- 

 ent within and without. The difference of pressure is near- 

 ly independent of the thickness of the porous partition, and 

 is attained in a space of time varying with the amount of 

 surface of the partition. Fourth. The difference of pressure 

 that the hygrometric diffusion is capable of producing and 

 of maintaining depends, other things being equal, on the 

 thickness of the partition. For porous earth, the possible 

 differences of pressure are very nearly inversely propor- 

 tional to the square roots of the thicknesses. Fifth. The 

 current of diffusion attains its greatest velocity when 

 the barometric pressure is the same on both sides of the 

 partition, and is greatest when the thickness of the par- 

 tition is least. Sixth. When the hygrometric diffusion 

 has brought about a difference of pressure within and 

 without the inclosure, the excess of volume of the prevail- 

 ing current is diminished in proportion as the difference of 

 pressure increases. This diminution is more rapid accord- 

 ing as the partition is thinner. Bulletin Soc. Vaiidoise, 

 Xausan7ie,18l5,Q0S. 



THE SEVERE STOEM OF MARCH 12, 1876. 



The severest storm that has ever been observed at Brussels 

 occurred on the 12th of March, 1876, on which occasion the 

 barometer fell to a very low point and the wind acquired un- 

 equalled violence. Its maximum force, as measured by the 

 pressure anemometer, w^as 144 kilogrammes per square 

 meter. On account of the exceptional character of this 

 storm, the director of the observatory, M. E. Quetelet, has 

 presented to the Royal Academy of Belgium a special study 

 of its history, development, and progress. Quetelet states 



