Mr. H. F. Morley on Grove's Gas-Battery. 277 



except between B and C, where it is conic. I assumed that 

 there is no discontinuity, and that the electromotive force is 

 proportional to the mean quantity of hydrogen in any layer 

 between B and C, or, what is the same thing, to the total 

 quantity between those limits, and that the current is propor- 

 tional to the total quantity destroyed per second. Hence I 

 deduced the formula 



(l + na)G=b-(c + nd)E; 

 where a, b, c, d are constants depending on the lengths BC, 

 CD, on the rate of escape of gas at D &c. The layer A was 

 assumed to be always saturated. In the actual experiment the 

 shape of the plates was by no means regular ; and even had they 

 been quite regular, the assumption that the whole of each ho- 

 rizontal layer is a uniform solution is far from the truth. So 

 I wrote the formula in a little more general form, 



(l+na)G=b + ne— (c + nd)E. 



If in this we put a = '0006, 5 = 244*5, e= -3-2, c='00725, 

 d— — -0000715, we get the last column (called " C calc") given 

 above. We should expect the last two results to be higher than 

 the calculated values, since no allowance has been made for 

 the capillary film rising round the emerging platinum. How- 

 ever, the formula evidently cannot hold for depths much greater 

 than 63, and it would become necessary to introduce terms 

 varying as n 2 &c. 



VI. From the above Table it is clear that the electromotive 

 force is not constant, as in ordinary voltaic cells, but rises with 

 the resistance. The same thing happens with ordinary gas- 

 couples with platinized platinum. In one case, changing the 

 external resistance from 46 to 10,000 only lowered the current 

 from 423 to 157 ; in another case, changing resistance from 

 10,000 to 190,000 lowered the current from 690 to 140. 



When the resistance is suddenly increased the strength of 

 current suddenly falls, but it rises, at first quickly and after- 

 wards more slowly, to near its former value. For when the 

 resistance is increased the current falls by Ohm's law ; but it 

 now uses up less gas, so that the gas accumulates in the liquid, 

 and by so doing raises the electromotive force, and therefore 

 the current ; and this continues until equilibrium is attained. 



So when the resistance in circuit is diminished the current 

 rises suddenly, but afterwards falls to near its former value. 

 For the current rises by Ohm's law ; but the increased cur- 

 rent uses up more gas, and so impoverishes the liquid sur- 

 rounding the platinum, thereby diminishing the electromotive 

 force, and the current falls. 



These observations seem fatal to the hypothesis that the 



