Voltaic Batteries^ Sfc. 175 



the several positions intermediate between the distance of 24 

 inches and 12 from the zinc, but that at 12 inches a certain- 

 sized plate will give the amount sought for. 



Proceeding on in the same manner still nearer to the zinc, 

 the required amount will be obtained likewise at 10 inches and 

 at 8, but only by plates larger than that yielding the same 

 amount at 12; but at the distance of 6 inches again, as at 24, 

 it cannot be obtained by any sized plate that the dimensions 

 of the trough will allow to be tried; whilst at the remaining 

 successive positions between 6 inches and the zinc or stand- 

 sivd position, the required amount will be readily obtained by 

 plates gradually diminishing in size, as the positions approach 

 nearer to the zinc, till we again reach the first position of \ of 

 an inch, and consequently obtain the amount by a plate equal 

 in size to that first employed. 



137. I proceed now to the details of the experiments by 

 which these and the remaining results have been detected ; 

 and it will be borne in mind, that it is the relation between 

 the magnitudes of the two copper-plates — the standard and 

 the required plates — those by which the equal amount of 

 action is given, and the distances at which they are respect- 

 ively required, which is the result immediately sought for. 



1 38. As a specific example of this kind of investigation, I 

 select the following average instance, the details of which 

 being given separately, will contribute to the better apprehen- 

 sion of the kind of results which are to be more fully embodied 

 in the succeeding tables. 



139. The small standard couple, with its copper plate at the 

 relative distance of |- of an inch from the zinc, gives the usual 

 measure of j—th of a cubic inch of hydrogen in 85 seconds; but 

 removed to the distance of 10 inches, the time required is 160 

 seconds. Then, in the place of the smaller copper plate, and 

 at the distance of 10 inches, are substituted other copper plates 

 in succession, and progressively larger, when the time in which 

 each yields the measure of hydrogen is as follows. 



Table (No. 7). 

 At ^ inch At 10 inches distance, 



distance. 

 Total surface in"| 

 square inches of \- 2. 2. 4. 8. 12. 18. 24. 32. 40. 



each copper-plate.J 

 Time in seconds ^ 

 in which each yields 

 the equal measure 

 of hydrogen. ^ 



140. Now it will be remembered always, that the fewer the 



85' 



160" 120" 1 10" 90" 85" 80" 



