368 Mr. 0. J. Lodge on a Mechanical Illustration 



gen in this time ; then, if M is the mass of the liquid and con- 

 taining vessel, the vessel will apparently be kicked backwards 

 with an initial velocity v f , where 



M.v' + mv-$mv=0 (1) 



Now suppose the containing vessel to be a cylinder of which 

 the electrodes form the ends, each of area a, at a distance apart 

 equal to d ; let p be the density of the electrolytic liquid ; and 

 let g' be the maximum density of the electrolyzable hydrogen in 

 the liquid — that is, the mass, per cubic centimetre of the liquid, 

 of hydrogen actually in motion near the cathode under the in- 

 fluence of the current. Then, if h cubic centimetres of hydro- 

 gen gas at the density cr be liberated per second by the current 

 when constant, the mass of this hydrogen will be 



h<r=avo J (2) 



The average density of the electrolyzable hydrogen may be con- 

 sidered as \<r r \ so the whole mass of hydrogen set in motion 

 through the liquid is 



«d*>=^, (3) 



1 



2— - 2v , 



while the mass of liquid and containing vessel 



M = adp + fj,. 

 Hence, neglecting the mass //. of the containing vessel, 



, Imv 7 her ,' 



This velocity would be extremely small; but it may be worth 

 looking for. The electrolytic cell should have the plates small, 

 because their area occurs in the denominator of (4), and it 

 should be suspended at the end of a short counterpoised tor- 

 sion-arm. Any twisting of the suspending thread might be 

 observed with a mirror and scale. The current should not be 

 allowed to last long enough to evolve any gas; or the reaction 

 of the rising gas might swamp the effect looked for. The 

 best plan would seem to be to reverse the current at regular 

 short periods corresponding with the previously ascertained 

 period of oscillation of the torsion-arm. The impulses vrould 

 then accumulate, and the gas would not form on the plates in 

 any quantity. 



The connexion indicated by (2) between the velocity of elec- 

 tricity and the mass of moving electrolytic hydrogen in a 

 cubic centimetre of the electrolyte seems to be of interest, 



