488 



KEPOUT — 1884. 



i til 



iif 



thorn.' He considers the electrical effect brought about by the electro- 

 negative ion oxygen combining with the zinc and charging it negatively, 

 ■while some electro-positive ion combines with the copper and charges it 

 positively, 'though not unless the two metals are in sufficient proximity to 



overcome electrolytic diffusion ' [whatevov 

 that may mean as applied to this case]. 

 He thinks his mercury dropping experi- 

 ment in coal gas is conclusive as to the 

 equality of potential of metals in contact. 

 This, I fear, is rather rapid induction. I do 

 not see how it follows on his own hypothesis 

 that his arrangement is virtually a reversed 

 Lippmnn electrometer. 



Sir W. Thomson's dropping arrangements 

 or voltaic cells, in wliicli gravity does the 

 work instead of chemical action, are so wi'li 



known that it is scarcely necessary to 



(!0 



more than refer to them. ^Ir. Hart's mor- 



rury dropper is scarcely a mcdificatio;i of 



the coppor-fding dropper shown in fig, ]'2. 



Fig. 12.— Thomson's Gravilal ion Sir William also shows how to couple up 



such cells in series,^ and how to constrain 

 r receiver. a mechanical rcplcnisher on the Vnlta 



Voltaic Cell 

 II copper filings. _ 



/. inductor-zinc. ,/ copper lunn.i. j^j.j ~ ipje "(fig; 13)'. 



'^"'l.i,n3Llll^"?,;^r-'\u'''*''''h- ' 6. In order to give this historical skotcl) 

 cnarjicd ii^j.-inist electrical torccs. It i -^ i 



yon join c iimu/ l)v a copper wire more completeness, it may be as well to 

 you ('.111 Ki't a current tiowing I'ocord rapidly such other memoirs as 1 

 wholly thron,.!, and with copper, j,^^,^ ^^^^ ^^^^ ^o get acquainted with : it 



is in the highest degree probable that several arc omitted, but; I hopo 

 no very important ones. Professor Wiedemann's collection of views ami 



I'ic. i;i. 'i'lionison's Vdltaic Induction Machine. 



()ne of tlio nidiii'tors r is lined with one nieta), the other with niiother, and the two C(inri.^"fi?. 

 The currier wheel i> mtated, .•ind the eoutai't sprinjrs A a' become oppositely charf^ed. By 

 afterward'* eliar;;iii;X t hi' inductors with a Daniell cell, and conipariii;; the delloctioi! :i(w 

 )trodueed in an electrotneler connected Id A a' with what it was hefore, measurements di 

 Volta ctlect can he obtaiiieil ; or of cours' it can be made a null method. 



memoirs bearing; on the subject is at the end of the second volume of flie 

 new edition of his ■ l^lektiieitiit.' 



Edlund has |)ublished a long paper"* in which he investigates expcvi- 

 mentally the Peltier elTcLl ; he points out clearly at the end that there is 



' Tlic (liaaranis of jintcntial wliich Mr. Ilavt gives of colls were criven more full," 

 by Prof . Kxnor in liis jiaprrim the Tlifory of Galvanic Elements, 1880. Mr. Hart- 

 views .are, in fact, rather similar to sonii- tif the more reasonable ones of Prof. E.xncr. 



- Elficirositaiic ItijiriiitK, \\. ;tL'.">. 

 - » Edlund: Pthjij. .\ini. c.xx.wii. 171; 0x1.43;'): oxliii. 101, •>'^\. See also VM. 

 Mag. (J) xxxviii. L'i;;! ; xliii. 81, 21:!, L'Ol ; especially p. 27:!. 



