LABORATORY NOTES. 295 



Professor Tnit's students in the l^hysicnl T/il)ornt(~)rv of Edinhuro-li 

 University some fifteen ^^ears ao;o. The position of Ihe C^ohalt line, so 

 I'onnd, was o'iven alonof with the positions of certain alloys in a ])a])er 

 1)V Professor J. Gordon ^lacGreg'or and myself ])ul)Iished in ihe 

 Transactions of the Poyal Society of Edinhnr£;-li, A'ol. XXVIIT (1878). 

 The particidar specimen of Cohalt used in tliese early experiments wa« 

 a short rod ohtained hy electrol^^tic deposition. The noteworthy ficts 

 reo'archn«^'' its thermoelectric line were that it lav helow nickel on the 

 diagram, and that its inclination to tlie lead line was mnch u'reater 

 than the inclinations of the iron and nickel lines. 



As a Lahoratorv exercise I gave to ]\Ir. Sawada, one of onr stu- 

 dents of physics, the task of studyin!^ tlie thermoelectric properties of 

 the sheet cohalt descrihed in tlie precedinii; note. The plan ado])tcd 

 was to f'irm a nudtiple arc of Palladium and Pismuth and ])v ])roper 

 adjustment of tlie resistances in these l)ranclies to ohtain an inter- 

 mediate line which should cut thrcnig-h the cohalt line at tempérai ures 

 within easy reach. 



Such an iiitermediate line passes tlu'ougli the neutral point of the 

 component metals. It di\ides the region hetween Iheir lines so that 

 any transversal is cut into ])(^rtions which are directly as the resistances 

 in the Ijranches of the nndti|)le arc. Thus hy varying the ratio of the 

 resistances in tliese hranches we may sweep through the region hetween 

 the two coi'responding diagram lines, interpolating so to speak any 

 iiitermediate line suitahle lor our pur])ose. The extreme accuracy with 

 which we can measure elc'tric resistance enahles us to fix the position 

 of this intermediate line a.s a.'-curately as the positions of the component 

 lines are known. 



The low jiosition of cohalt on the diagram very much circum- 

 scrihed the choice of metals for the multiple arc. lîisnuith had to he 

 one of them, as it alone was known to he heh^w cohalt. The other 



