516 



iiEroRT — 1884. 



I'M 



the other plates one after the other, making the current as nearly the 

 same each time as convenient (by adjusting resistance) and allowing for 

 outstanding discrepancies. An amperemeter placed in circuit measured the 

 current, and the voltameter used was a reflecting galvanometer with some 

 30,000 ohms in its circuit. Its indications Averc interpreted absolutely In- 

 tapping off, at the same time as the cells, the difference of potential between 

 the terminals of an ohm (or 4 or ^ ohm) coil placed in .the circuit. 



Any two values of the strength of current enabled the internal 

 resistance of the cell to be calculated, provided its E.M.F. remained con- 

 stant. With low currents it did sjem to be fairly constant, and a mean 

 value of the internal resistance ;• is reckoned from these as V ohm. 



The area of each plate under the liquid was exactly the same, and 

 measured 3 inches by 2^ inches. Both faces of each phite were exposed, 

 though naturally one face was more active than the other. 



The arithmetical reductions are rather long ; the results ai*e all that I 

 give. It Avill be perceived they are anomalous in places, a great deal of 

 this being dependent on whether the reading of ]*j.]\I.F. was taken soon 

 after a current- change or not. As I said before, the plan of experiment is 

 avowedly rough, though the actual readings Avero carefully taken ; but 

 without understanding more about the circumstances of the case, and 

 Avhat possibilities of variation there are, I do not see how to plan a 

 perfect sj'stem of experiment on the subject. 



I will first give relative numbers, simply comparing the differences of 

 potential betAveen the terminals of the three cells Avhen the same current 

 is going through each, the resistance of each being the same, viz. 

 I ohm ; and then I Avill interpret the obserA-ations absolutely, calculating 

 the E.M.F. of the cell under different currents, and seeing what empirical 

 formula will best fit it. 



Tielaiivo differences of fntential hefween the terminals of three rolfamefcrs of 

 the same resistance, tliroufjh each of which the same current is driven hit 



an auxiliary battery, 

 f latinum respective ly . 



A)i,ode of each cell, nnc; cathode, zinc-copper aiiii 



In the above table the difference of potential between the terminals is 

 written negative when it opposes the current, and positive when it helps 

 it on. 



Wo Avill now interpret similar measurements absolutely, reckoning 

 the actual E.M.F. of each cell, and try to fit an empirical formula to it on 

 tlie plan of those (in sect. 20) already guessed; assuming /(C) a linear 



