474 Intelligence and Miscellaneous Articles. 



(Sitz. Akad. Wim, xlix. 2, p. 229) and by Beetz, using a modifica- 

 tion of the method of compensation (Pogg. Ann. cxlii. p. 581, 1871). 

 Apparently, however, physicists generally are under the impression 

 that the diminution in E.M.F., or "polarization" of the cell, thus 

 produced is practically inappreciable : thus, for instance, within the 

 last few months a determination of the value of v has been made 

 in SirW. Thomson's laboratory by E. Shida, by measuring the 

 E.M.F. of a gravity Daniell, first, in electrostatic units (no current 

 being generated), and then in electromagnetic units (a moderately 

 powerful current being set up) ; the which method evidently can 

 only be applied if the difference in the E.M.F. according as a cur- 

 rent is generated or not is negligible (Brit. Assoc. Eeports, 1880, 

 p. 497). The same kind of remark applies to several other inves- 

 tigations published during the last few years." 



With reference to the above remark on my paper, I have to state 

 that I knew quite well that the calculation of an E.M.F. may be 

 vitiated by "polarization" (a well-known phenomenon), but that 

 when the external resistance is great compared with the internal 

 resistance of the cell, as was the case in the determination of the 

 E.M.F. of a Thomson gravity Daniell, described in my paper, the 

 alteration in the E.M.F. due to "polarization" is so small, if 

 any thing, as to be negligible. It would have been better, however, 

 had I not omitted to mention that what I really depended upon was 

 the measurement (performed both electromagnetically and electro- 

 statically) of the E.M.F. of the cell ivliile the current iv as actually 

 flowing through the tangent-galvanometer. The result confirmed 

 perfectly the calculation according to " Ohm's law " on the sup- 

 position of constant E.M.F. and constant resistance, which I gave 

 in my paper, and which I adopted only after this confirmation. 



ON THE PRINCIPLE OF THE CONSERVATION OF ELECTRICITY. 

 BY G. LIPPMANN*. 



The quantity of matter and the quantity of energy are not the 

 only magnitudes which remain constant : the quantity of electricity 

 enjoys the same property. If we consider any (electrical) pheno- 

 menon in its entirety, we perceive that the distribution of the elec- 

 tricity may change, but that the sum of the quantities of free elec- 

 tricity never varies. If the electric charge experiences a positive 

 variation at certain points, it experiences at other points a negative 

 variation ; and the algebraic sum of all the simultaneous variations of 

 the charge is always zero. The sum of the quantities of free electri- 

 city is then constant, since its total variation is always equal to 

 zero. This law, which 1 call the principle of the conservation of 

 electricity, extends over all the phenomena hitherto studied; it 

 results from old and well-known experiments of which the mention 

 is sufficient. Thus, in the case of the sharing of a charge between 

 two bodies, we know that the total charge remains the same after 

 redistribution as before. It is the same in the case of friction : we 



* Translated from the Comptes Rcndus, t. xcii, No. 18 ; p. 1049 ; May 2, 

 1881. 



