﻿206 Prof. W. Ramsay on the Passage of 



and the components of the force on the pole itself at any 

 time t are found by multiplying these expressions by the 

 strength of the pole, i. e. by f(t\ and putting #=£•(*), y = rj{t), 

 - = ?(£) after the differentiations have been performed. 



In particular, if the pole moves along a straight line per- 

 pendicular to the plate, and we take this line as axis of z, the 

 force on the moving pole itself 



=™* {mr- 2n L im + ^ + %-^ }- (23) 



The well-known case in which a pole is suddenly generated 

 at the time £=0, and its strength remains constant and equal 

 to m after that time, is deduced by making 



/(0=0 from £=-oo to t = 0, 

 f(t)=m from t = to t=+co. 



We therefore have to write m for f(t) in the above ex- 

 pressions and to reduce the inferior limit of integration with 

 respect to t from — qo to 0. 



The advantage of starting with a fixed instead of a moving 

 pole is more evident in the case of a cylindrical or spherical 

 sheet, especially in the latter, since we are thus enabled 

 to use zonal spherical harmonics only and the analysis is 

 consequently much simplified. 



XXII. The Passage of Hydrogen through a Palladium Septum, 

 and the Pressure which it produces. By William Ramsay, 

 F.R.S. * 



IT has been frequently cited as an argument in favour of 

 attributing the osmotic pressure exercised by a substance 

 in dilute solution on the walls of a vessel permeable to the 

 solvent but not to the dissolved substance, that if a vessel 

 were constructed of palladium, which, as Graham's researches 

 showed, is permeable to hydrogen, but not to many other 

 gases, such a vessel would be subjected on its interior walls to 

 a high pressure if it were filled with an indifferent gas and 

 exposed on its exterior to an atmosphere of hydrogen. The 

 gas confined in the vessel, not being able to escape, would 

 exert the pressure at which it was allowed to enter ; while 



* Communicated by the Physical Society : read May 25, 1894. 



