Intelligence and Miscellaneous Articles. 451 



12. The behaviour of mechanically deformed or magnetized bodies 

 is different in changes of temperature, in which relations of this 

 kind after accommodation of the molecules are no longer clearly 

 apparent. 



A LECTURE EXPERIMENT ON THE DIFFUSION OF GASES, 

 BY A. WINKELMANN. 



On the occasion of experiments which were intended to deter- 

 mine the tension of elastic vapour in spaces filled with gas, I 

 made the observation that the pressure of the vapour only became 

 constant after the lapse of a very long time. If into a tube over 

 mercury containing air under a pressure of about 0*300 millim. an 

 excess of liquid be introduced, the vapour does not at once fill the 

 space above the mercury. This only takes place slowly in accord- 

 ance with the progress of the diffusion of vapours in the air above. 

 As long as the density of the vapour is not everywhere the same, 

 the pressure of the mixture of gas and vapour is not a maximum. 



This method may be well used to show the difference between the 

 velocity of diffusion in various gases, for instance air and hydrogen, 

 l^ith this view air and hydrogen are filled into two equally long 

 barometer-tubes so that the mercury is at the same height. If 

 then ether in excess is added to each tube, the mercury sinks more 

 rapidly in the tube containing hydrogen, and after a few minutes 

 the tubes show a marked difference in pressure, as is seen from the 

 following numbers, which were obtained at a temperature of about 

 15°:— 



Height of the Mercury. 



Time, in Air, Hydrogen, Difference. 



minutes.. millim. millim. millim. 



without the ether 449 449 



2 with the ether 361 346 15 



4 „ „ 359 332 27 



8 „ „ 355 316 40 



18 „ „ 332 280 52 



Hence ether vapour diffuses far more rapidly in hydrogen than 

 in air. 



Ultimately the difference of pressure in the two tubes diminishes 

 and becomes zero. This lasts some time, for after two hours the 

 difference was still 30 mm. — "Wiedemann's Annalen, No. 3, 1886. 



ON VAPOUR AND MIST. BY ROBERT YON HELMHOLTZ. 



The final results of the experiments and arguments on the for. 

 mation of mist are stated by the author as follows : — 



The formation of mist in moist air does not exactly coincide with 

 the occurrence of normal saturation, but with one somewhat 

 greater. This is partly due to the fact that there is greater tension 

 over convex vesicles than over plane surfaces. 



The formation of mist, at any rate after introducing a correction. 



