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X.— Researches in Contact Electricity: Thesis for the Degree of Doctor of 
Science. By Careitt G. Knorr, D.Sc. Communicated by Professor 
Tair. (Plate X VIL.) 
(Received July 23d ; revised October 27th, 1879). 
At the surface of separation of any two. different substances in contact, 
there exists in general an electromotive force tending to maintain a certain 
difference of potential between them. This principle, established for metals by 
VotTA in 1796, has been extended by later investigators to other substances, 
including liquids and gases. From these early researches of Vouita,* and the 
later more elaborate inquiries of KonirAuscu,t HANKEL,{ and GERLAND, § 
there have been deduced certain fundamental laws, which have been fully 
corroborated by the recent work of CuiFrTon, || and Ayrron and Perry. If, 
of a number of conductors set serially in contact, the difference of potential 
between each successive pair is quantitatively estimated and reckoned positive 
or negative, according as the first member of the pair is at a higher or lower 
potential than its successor, then the difference of potential between the first 
and last members of the chain is equal to the algebraic sum of the potential 
differences between the successive contiguous pairs. Should the series be made 
up of simple conductors, the potential difference between the extremities is 
quite independent of the nature, number, and order of the intervening com- 
ponents, and is, indeed, equal to the difference obtained by direct contact of 
these extreme members. Hence, in a circuit composed of such substances 
(metals for example) and kept at a uniform temperature throughout, the sum 
of the differences of potential existing at the various surfaces of contact taken 
in order all round the circuit is zero. The resultant electromotive force is 
therefore also nz/, and no current can exist. This result of experiment is in full 
- accordance with the recognised principle of the conservation of energy, there 
being in these circumstances no source from which the current could derive its 
energy. Should the contact-chain, however, consist partly of compound or 
chemically decomposable: conductors, the potential difference between the 
* Annales de Chimie, vol. xl. p. 225 (1801); also WiepEmann’s “ Galvanismus,” vol. i. §§ 1-7 
and 14. 
; + Poggendorff’s Annalen, vol. Ixxxii. p. 1 (1851), and vol. Ixxxviii, p. 465 (1853). 
t Ibid., vol. exv. p. 57 (1862), and vol. exxvi. p. 286 (1865). 
§ Ibid., vol. exxxiii. p. 513 (1868). 
|| Proceedings of the Royal Society (London), vol. xxvi. (1877). 
 Jbid., vols. xxvii. (1878), and xxviii. (1879). 
VOL. XXX. PART I, 25 
