142 
PROFESSOR DANIELL ON VOLTAIC COMBINATIONS. 
amount. The area of the mean section of the electrolyte would be the area of a cy- 
linder placed half way between the cylinder and its axis, or half that of the cylinder ; 
and it would be the same whether the generating or the conducting metal were the 
exterior of the two. 
Now the amount of the current ought to be the same whatever might be the dia- 
meter of the exterior cylinder, for the resistance occasioned by increasing the depth 
of the electrolyte, that is to say, by increasing the radius of the cylinder, is exactly 
counterbalanced by the increased conducting power conferred by the increased area 
of the section of the electrolyte, and vice versa. The results of the experiments con- 
firm this conclusion ; for upon reference to Table I. it will be seen that cylinders 
of 1 J inch and 2§ inches diameter produced, under like circumstances, the same 
amount of current ; and from Table II. we learn that cylinders of 2f inches and 5| 
inches diameter had equal influences. 
You may perhaps remember, that in my former communications, from some 
experiments upon this point*, I had obtained some anomalous results which occa- 
sioned me considerable perplexity, but I have since multiplied observations suffi- 
ciently to place the confirmation of the law beyond a doubt. 
Amongst others, I repeated the experiments with the large battery of ten cells of 
four inches diameter, in comparison with ten of 3| inches, and found the results sen- 
sibly the same. The origin of the error in my former observations I have been unable 
to detect ; but it is probably to be ascribed to some fault in the connections of the cells. 
The advantages of the concentric cylindrical arrangement of the elements of a 
voltaic circuit are very considerable ; both in the scientific analysis of its complex 
actions and in its practical applications. The absolute restriction of the influence of 
the metallic plates to one side respectively, and the known definite relations of their 
surfaces and diameters, render the necessary calculations for the former obvious and 
easy ; while for the latter, the reduction of the size of the generating metal, and the 
large quantity of the electrolyte which it admits of, give facilities for the maintenance 
of an energetic and constant current of force which no other arrangement can supply 
with equal effect. 
I have already observed-^ that the position of the rod within the cylinder is imma- 
terial to the effects, and it is obvious, that wherever placed, their mean distances, and 
consequently the mean section of the interposed electrolyte, must be the same. 
A zinc rod of half an inch in diameter, placed in the axis of a copper cylinder 
inches diameter, produces a certain effect, which is scarcely augmented in an appre- 
ciable degree by a second, or even a third similar rod placed in contact with it : the 
results of experiment were as follows : — 
1 rod = 2-2 
2 rods = 2*4 
3 rods = 2'5 
* Philosophical Transactions, 1839, p. 90. 
f Ibid. 1838, pp. 44, 49. 
