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' Von Mni 



von Znlin, tho litllo too-nii.vpd-iip oliHcrvatioii of .Mr. Hurt (tli'scril)(!<l 

 later), tho incasnninonts of Schult/.i'-Mciyc, and tlic nioro dfi-idcd ex- 

 perimonts of Urown, It nmy indeed ho readily held I hat tho weight of 

 experimental evidenee tends f lie other way, since most experimontcrs on 

 ilie subject — I'clliit, Schul(ze-Mer;;-e. voii /aim, and, I niiiy add, Sir 

 William 'J'lioniso!! — have lel't oil" ju^t as pine eontaet theorists as they 

 liej,'nii. [ would attempt an experiment niysclf, save that I mil so ])ro. 

 tbunilly impressed with tho dillieiilty of makiiiji; one in which no fault 

 or loophole can he found, and which will by everyone Iio deemed satis- 

 factory and iinal ; so I prefer to base my views on a 'general survey, 

 and on fairly conclusivo reasoning, rather than on a crucial but alinosl 

 ini])ossil)lo experiment. 



■'.. Perhaps this is now the place to ri'fer lo the somewhat erratic; 

 series of papers by Professor Franz Kxner, of Vienna.' He m,'*s him- 

 Bolf to disprove tlio existence of contact force in the most straigiit- 

 forward and obvious manner, and to establish tho fact that there is no 

 electrical evolution without deliiiito and actual chemical action. To this 

 end he announces the followin^j;' propositions: (1) that two metals in a 

 clieniically indifferent medium show no electricity : ("2) that tho potential 

 (litference of two eoiineeted metals in air is exactly half the diiferenco of 

 their heat combustion energies ; and (o) that two pieces of tho same metal 

 produc(> contact electricity as soon as tl'ey are i>ut into <diemically 

 different atmospheres. 



Tho experiments by •which ho supports these assertions have, every 

 one of them, been elaborately and severely c;Mticised by J5eet/, Jloorwe^-, 

 Julius, Schultze-iJcrgc, vmi /'aim, Ayrton and Poi-ry, IVllat, and VViedc- 

 niiinn ; and his numerical determinations of contact force appear to bo 

 iiiii(iue,''^ 



It is not necessary for mc to enter into a discussion on tho merit of 

 his experiments, inasmuch as the mere fact of tlio exi.stence of so great a, 

 body of hostile opinion is sufficient to show that they arc not of a kind best 

 qualilied to ])roduco conviction. The theoretical views which led Professor 

 Kxncr to formulate his second statement above, that tho potential dif- 

 ference of two connected metals is eipial to half tlie difference of their heats 

 of combustion per equivalent, sire, 1 am sorry to say, (piite unintelligible 

 to mo. They depend on tho hypothctically necessary existence of films 

 of oxide, between which and the metal there is suppo.sed to boa consider- 

 able difference of potential. IVrhajis a few (juotatious I'rom Professor 

 Kxner's first paper on contact electricity will render his position clearer,'* 



' Kxncr: Sif:h. i/ir Alind. ilcr ]Vi.i^r>)i>f/i. Wicn : .Inly IS7S, ' On tho Nature of 

 (ialvanic rolaviwitiou ' ; July 1S7I>, 'On thct'iiuse ol" tlic I'roiluetioii of K. by tin- 

 lontact of nct(!roi:;cneous ^Ictals' ; Dei'. 187H, ' On the Thciiry of inconstant, (ialvanir 

 Klemcnt;! " ; May 18S0, ' On tho Theory of Volta's Fundiiincntal F.x])enniont ' ; July 

 1880, ' On tho Theory of Galvanic Kloiiionts ' ; Nov. 1880, ' On the Natiin; of (ialvanic 

 Polarisation ' ; July 1882, ' On soino Kxporiinents rrlatinfr to (. dntart 'I'iieory.' 



- Ilt'ct/, ; M'ii'/irmtnin'K Aiiiiii/cii, \u. L'ilO; Hoorwo;,'-, ihitl., \\. Kt.'t, 1880, and xii. 

 p. DO; Julius, (7>iV/., xiii. 270 and 21)0; ScIiultzc-Bor<ro, ?7/('rf., xv. 440, as well as xii. 

 :!07and;ill); von Zahn, p. 41 and 1 're face, of his iMomoir; Ayrton and IVrry, /'A//. 

 .1%. 1881, ]). 4:{ ; Pollat, Purls, 'J7ihe.% No. 461, p. 17; Wiedemann, h'lcltrivitat, it. 

 lt'J2-!)l»5. 



• I quote from llr. J l^rown'.s translation (Phil. Map., Oct. 1S80) of a paper by 

 Kxnor in Wiedemann'.s Aniialcn of the same year, with some abbreviations. ' An inves- 

 tis,'atinn concerning the nature of j;alvanic polarisation has led me to a quite distinct, 

 view of the origin of the so-called contact electricity, a view which will be supported 

 by experiments following. I have shown that the original cause of the polarisation 



