ELECTROMOTIVE FORCES IN THE VOLTAIC CELL. 489 



no relation between the Peltier and Volta effects, and he suggests that 

 this is becanse of the contact force between the metals and the gas or 

 air in which they are, the fact of such contact force being, he thinks, 

 sufficiently established by gas batteries and galvanic polarisation. 1 



Majocchi, in a paper printed in ' Phil. Mag.' xxx., p. 97, regards the 

 E.M.F. of contact as due to the ' adhesion ' of the two metals for each 

 other : pretty much the same idea as Sir Wm. Thomson's chemical action 

 at a distance, an idea which makes the energy of the Volta effect Zn/Ca 

 depend on and be calculable from the combination heat of zinc and copper- 

 in making brass. I mnst return to this matter later, because it is import- 

 ant in itself and crucial as regards theory. 



Gassiot 2 made an experiment intended to show that there could be a 

 difference of potential excited between metals by proximity withont 

 actual contact, or at any rate without metallic contact. Grove 3 also 

 made a similar experiment. 



Hoorweg 4 and also Nobili 5 have a theory that all galvanic currents 

 are really thermoelectric. 



In the article 'Electricity' in the ' Ency. Brit.' p. 99, Professor 

 Chrystal gives some clear general considerations regarding the seat o/ 

 E.M.F., and the opposing views which are held with regard to it. He is 

 judicial iu his attitude with regard to them, but the mere statement of 

 the position in so clear a form is in itself a powerful argument for the 

 views held by Maxwell. 6 



Pleeming Jenkin, in the last edition of his ' Electricity and Magnetism,' 

 p. 216, endeavours to reconcile the contact and chemical theories. Accord- 

 ing to the chemical theory the E.M.P. of a cell = 2 (J Be.) ; according to 

 the contact theory it is C/L + L/Z + Z/C. On these undoubted facts he 



1 Snndell investigates the E.M.F. of alloys in contact with copper, employing 

 Edlund's method, and finds, like him, that for alloys, as well as for simple metals, tin- 

 Peltier corresponds with the Seebeck force. The peculiar language used in this and 

 the preceding paper may easily cause it to be imagined that they have found Volta 

 force to agree with Peltier. In fact, Sundell is so quoted in Watt's 3rd Swppl., p. 708-. 

 Von Zahn quotes Edlund in the same sense, and indeed it is probable that Edlund 

 himself at first thought he was investigating Volta forces thermoelectrically.— 

 Sundell: Pogg. Ann. cxlix. HI 



1 GassiotY Phil. Mar/, xxv. 1841, p. 2S3. 



3 Grove : Literary Gazette, Jan. 21, 1S43. Wiedemann, Elec, ii. 988 



• Hoorweg: Wied. Ann. ix. 552, 1880; xi.p. 233, and xii. p. 75. 



5 Prof. Wiedemann notes, as interesting, that in 1828 Nobiliheld a notion that all 

 galvanic currents are thermoelectric, thus vaguely anticipating the modern thermc- 

 dynamic theory of E.M.F. See Wied., Electrieitat, ii. 985, and Nobili, Bill. Ihiir. 

 de Geneve, xxxvii., p. 118. But Prof. Hoorweg seems bitten with the same idea in 

 recent times, and in 1879-80 writes long papers in proof that all current energy ii 

 due to absorption of heat at junctions ! 



8 Although this article is, or ought to be, easily accessible to everybody, there is 

 one important suggestion in it which it is as well to quote, viz. that contained in the 

 following sentence : ' We are so ignorant of the nature of the motion which is the 

 essence of the electric current that the very form in which we have put the question 

 [as to the locality of the E.M.F.] may be misleading. If this motion be in the sur- 

 rounding medium, as there is great reason to believe it to be, it would not be 

 surprising to find that speculations as to the exact locality of the E.M.F. in the- 

 circuit were utterly wide of the mark.' Prof. Willard Gibbs suggested something of 

 the same sort at Montreal, though in a rather vaguer form. I do not myself feel any 

 doubt that a precise location can be given to the E.M.F., notwithstanding that much 

 of the current energy exists in the medium. The most complete attention to the 

 distribution of energy in circuits which has yet been bestowed on the subject has 

 been given by Prof. Poynting in his remarkable memoir, Phil. Trans., 1881, and he 

 therein locates the E.M.F. of a battery exactly where I do myself. 



