Voltaic Batteries, Sfc. l^l 



those which were obtained tjie latest of all from the experi- 

 ments gone through to determine the law of distance. No 

 reliance was placed upon the first attempts made to deter- 

 mine this question, nor upon any, till by innumerable repe- 

 titions of experiments, and a perfect familiarity with the pre- 

 cautions necessary to be observed in their course, I had be- 

 come assured that the whole were accurately performed, and 

 that by the regulations adopted every possible or probable 

 source of error likely to arise from the method here employed 

 was precluded. The above results may therefore be con- 

 sidered to show correctly the peculiar phaenomena attendant 

 upon voltaic action, in the kind of arrangement here brought 

 into action. 



97. The first consideration which naturally follows a re- 

 view of the above table, is that of the singular difference in 

 the effects of distance upon voltaic action ; as those effects 

 are determined by this method of experimenting, and those 

 already deduced by the indications of the magnetic needle. 

 Referring to the nearest authority at hand, I find that the law 

 of distance as determined by the needle is as follows : 



98. " The deflection produced by a pair of plates in an 

 acid solution of uniform strength varies inversely as the square 

 root of the distance between them, a law previously established 

 by Gumming. Thus, if a plate of zinc be placed successively 

 at 1, 4 and 9 inches from a plate of copper, the deflecting 

 powers will be in the ratio of 3, 2, and 1 ; that is, only twice 

 as great at 1 inch as at 4, and only three times as great at 

 1 inch as at 9*." 



99. As the magnetic galvanometer, of whatever construc- 

 tion, is employed as a measurer only of comparative quantities 

 of electricity, and not of the absolute quantity evolved by 

 any arrangement, it is in this relation merely that the indica- 

 tions of that instrument are now brought into comparison 

 with those afforded by the method here used for the same 

 purpose. When the quantities of electricity evolved at the 

 several distances are estimated by the indications of the 

 needle (that is, by their power to deflect the needle, in op- 

 position to the power of the earth's magnetism, or to any other 

 power substituted for it, as in the torsion galvanometer) then 

 those quantities differ from one another by the rate just stated ; 

 but when estimated directly by the quantities of matter ex- 

 pended in producing them (on which principle the plan now 

 used is founded), then they differ from one another at these 

 several distances by a rate totally different from that de- 



* Dr. Ritchie. 



