^ 1. 2. 4. 6. 8. 10. 12. 



>132'' 1S5" 142'^ 143'^ 147^' 154" 159'^ 



Voltaic Batteries, 8fc. 71 



at the depth of one inch from the surface of the liquid, and 

 afterwards at the bottom or at the depth of 12 inches, but 

 still at the same lateral distance from the zinc, the quantity of 

 voltaic action obtained at each of these positions will be found 

 widely different, as will be seen by the following table, in 

 which the copper plate is moved through the same vertical 

 plane to the different depths successively : 



• No. 3. 

 Depth in inches of~ 

 the copper plate 

 from the surface 

 of the liquid 



Time, in seconds,' 

 needed at each 

 depth to yield 

 an equal mea- 

 sure of hydro- 

 gen ... ._ 



57. When the plate is near the surface of the liquid the 

 hydrogen arises from it in a regular stream of exceedingly 

 minute bubbles ; but when at a greater depth they are dis- 

 missed from the plate irregularly and of a much greater size, 

 having apparently adhered to it longer and with greater te- 

 nacity than when nearer the surface. It is easy to conceive 

 that previously to the dismissal of these larger bubbles from 

 the surface of the plate, they will have prevented the direct 

 contact of the acid and the copper by an interposed stratum 

 of air, proportionate to the size of their bases, and hence have 

 impeded the voltaic action itself. That these differences are 

 due solely to the influence of pressure, in the present case, 

 will be more distinctly shown subsequently (section 7th), when 

 the precise relative positions of the two plates in these trials 

 will need to be remembered. 



58. We perceive in the foregoing enumeration a variety of 

 minute influences and effects, incessantly obtruding themselves 

 into examinations of the nature of this present inquiry ; all of 

 which, with the utmost care, need to be provided against, or 

 as far as possible to be corrected, to ensure any degree of ac- 

 curacy in the results of experiments. 



59. For the sake of a compendious reference to the methods 

 by which these sources of error are obviated, or their effects 

 otherwise guarded against throughout this inquiry, they may 

 be classified as follows : 



60. 1st. Circumstances merely mechanical, affecting the 



