C. GENERAL PHYSICS. 173 



ence of the vapor of water. The extent of the variation of 

 temperature which accompanies diffusion is different in dif- 

 ferent cases, according to the special arrangements of the 

 experiments. It is always greatest when the diffusion is 

 most abundant and most active. We can conveniently 

 explain the facts established by supposing that in the dif- 

 fusion the gaseous current produces a heating on the side 

 where it comes into the porous partition, and a cooling on 

 the side where it emerges. These currents having an un- 

 equal importance, depending on their density, we can com- 

 prehend that there is, as a result, a warming on one of 'the 

 faces, and a cooling on the other face of the partition. 

 When the experiments are made under different barometric 

 pressures, we find that, when the endosmose of a lighter gas 

 is accompanied by an increase of pressure in the porous 

 vase, the temperature varies only very little, and generally 

 augments during the endosmose, while the manometer falls 

 after having attained its maximum, and the pressures tend 

 to equalize themselves, the temperature diminishes more or 

 less rapidly, and by a relatively considerable quantity. 

 When the exosmose of a lighter gas gives rise to a diminu- 

 tion of pressure in the porous vase, the temperature varies 

 only a very little, and more generally diminishes during the 

 exosmose. When the manometer rises after having attained 

 its maximum, and the pressures tend to equalize themselves, 

 the temperature augments more or less rapidly, and by a 

 quantity relatively quite considerable. This change of tem- 

 perature, when the diffusion is accompanied with a change 

 of pressure, is conveniently explained by admitting that the 

 thermic variation due to the diffusion is conformable to the 

 laws above indicated, and is due (but with a certain re- 

 tardation) to the variation caused by the compression or 

 the ratification of the gas which surrounds the thermometer. 

 Bibl Univ., XLIX.,lo3. 



ATTRACTION, REPULSION, AND RADIATION. 



Professor Crookes, whose first interesting paper on radia- 

 tion was read in 1873, has recently made a second communi- 

 cation on the subject, in which are described certain im- 

 provements introduced by him, and new forms of apparatus, 

 which enable the phenomena of repulsion by radiation to be 



