166 TRANSACTIONS OF THE SOCIETY OF PHYSICS AND 



designed especially for sea-soundings of great depth. This instrument 

 consists essentially of two spherical reservoirs, superposed and con- 

 nected by a capillary tube. The upper reservoir should be closed and 

 entirely filled with a compressible liquid, for example alcohol ; the other, 

 which has an opening in the upper part, must be full of mercury, which 

 ought also to fill the capillary tube. The quantity of mercury which 

 will pass from the second reservoir into the first when the apparatus is 

 submitted to pressure will give the measure of this pressure, and con- 

 sequently of the height of the column of water, or, in other words, of it& 

 depth. 



M. Archard described a manometer of precision, of his invention, con- 

 sisting of two liquids, water and petroleum. His memoir, accompanied 

 with a plate, was published in the Archives of Physical and Natural 

 Science, for April, 1874. 



M. Achille Cazin, honorary member of our society, on a visit to Gen- 

 eva, entertained us with some recent researches on the thermal phe- 

 nomena which take place in a magnetic circuit, an extract of which 

 appeared in the Comptes Eendus of the Academy of Sciences. 



The last work of our illustrious colleague, Auguste de la Rive, was 

 accomplished in association with M. Edouard Sarasin, who gave the re- 

 sults in the session of the 20th of November last. He investigated the 

 action of magnetism upon the electric discharge in rarefied gas, when 

 this discharge takes place in the prolongation of the axis of the mag- 

 net. In this case the magnet produces a considerable augmentation of 

 the current, when it acts directly upon the negative electrode. It seems, 

 from these experiments, that there is a special and very strong resist- 

 ance proceeding from the negative electrode, which the action of the 

 magnet serves to overcome. {Archives des Sciences physiques et naturelles, 

 April number, 1874.) 



M. Eaoul Pictet communicated to us several series of observations 

 which he had an opportunity of making, during a long sojourn in Cairo, 

 as director of the physical cabinet of that city. To speak first of those 

 which treat more particularly of physics, he found, by means of a large 

 actinometer, the measure of the intensity of the calorific radiation at 

 Cairo. His apparatus consisted of a kind of caldron or boiler, formed of 

 two thin ])arallel plates of iron, which was filled with water, and placed 

 in a case full of cotton. This case was blackened, and closed at the side 

 turned toward the sun by a variable number of glass plates. It results 

 from these observations that in Egypt a surface of a square meter, ex- 

 posed normally to the rays of the sun, in the middle of the day, absorbs 

 nearly twelve calories a minute. Other observers in Europe find under 

 like circumstances that the absorption amounts to about six calories. 

 The diurnal evaporation produced under the action of the sun is about 

 one-sixth of an inch of water ; that which results IVoni dry air iuid 

 from wind is about three-sixths of an inch. 



M. Soret made several communications upon the phenomena of polar- 



