493 
Tiuo Fluidsy and of Two Metals not in Contact, 
alone, therefore, no measure for the difference of the electro- 
motive forces here entering into action, the determination of 
which, however, is the sole object of the present inquiry. I 
have therefore, in the following experiments, chiefly directed 
my attention to the accurate determination of the direction of the 
current; its relative intensity, being dependent on too many 
circumstances, is only given approximately : the magnitude of 
the deflections of the needle were, however, always carefully 
noted. 
M. Vorsselman de Heer, in his valuable memoir on Electric 
Telegraphy*, states of this numerator, after having observed 
that it depends on the nature of the metals, and not on their 
dimensions ; that its value is not altered when salts, alkalies, or 
acids, which, like sulphuric acid, or nitric acid, are not electro- 
lyzable, are added to the water ; but that it undergoes a change 
when the body which is added is itself an electrolyte, for in- 
stance hydrochloric acid, in which case the numerator would 
be smaller. 
According to Faraday, who, however, is not acquainted with 
Ohm’s theory, this numerator would be greater, the stronger 
the^ affinity of the positive metal, the zinc, is for the oxygen, 
chlorine, or electro-negative constituent of the fluid in general ; 
it must, however, be here observed, that we possess at present 
nothing more than approximate valuations from which we may 
judge of the energy of a chemical affinity. 
The main result of my experiments has proved in the most 
positive manner that the value of the numerator in OhmJ’s for- 
mula, or the magnitude of the electromotive force in general is 
altered, sometimes increased, sometimes diminished, by any sub- 
stance added to the water, be it an electrolyte or not, and indeed 
{which should be well observed) increased for one metal combina- 
tion, and diminished, for another, by the same substance, added to 
the water in the same proportion. 
Nor have I been able to find that this force stands in direct 
ratio to the energy of the affinity between the positive metal and 
the negative constituent of the fluid. It is weak in cases where 
this energy must be considered as strong, and on the contrary 
strong where but a weak affinity can be admitted. Frequently, 
indeed, a current originates, and at times a powerful one, ivhere, 
to judge from the affinity, not the slightest action should be ex- 
pected. 
Sufficient proofs of this will be found in the statements con- 
tained in the following Tables. 
To render these Tables intelligible, it may be observed that 
* PoggendorfTs Annalen, vob xlvi. p. 51G. 
