340 E. L. NICHOLS. 



Hereaus gave iu the hands of tlie présent writer .01826 volts at the 

 same température. Siemens ') aucl later, Callendau ~), aud his co- 

 workers liave showu the saine to be true iu platiuum thermoiuetry. 



To tliis eud^ uumerous more or less complicated methods iuvolving 

 tlie use of varions forms of the gas therinometer hâve been proposed, 

 the carrying ont of which involves the use of spécial apparatus which 

 is difïicult of construction and so laborious in opération^ as in many 

 cases to in volve a far greater expenditnre of time than is necessary for 

 the investigation in which the thermo-elements are to be employed. By 

 means of such apparatus in the haiids of tlie investigators already men- 

 tionedj and by the independent methods employed by Violle "'), the 

 melting points of copper, silver, gold^ palladium^ and platiuum hâve 

 been observed with a fairly satisfactory degree of accuracy; so that we 

 are now in position to use thèse melting températures as référence 

 points upon a calibration scale. Wide différences of o])inion still exist 

 conceruing the absolute values to be assigned to them, but a provisional 

 scale of températures nt least may thns be established for any thermo- 

 element for which the electromotive forces produced wheu the hot 

 junction is brought to the température of thèse raetals at their points of 

 fusion eau be determined. 



In the course of a récent séries of stndies ') on the acétylène llame;, 

 I hâve shown that this source of radiation possesses a température above 

 the melting point of platiuum and that it may be used for the détermi- 

 nation of the electromotive forces of platiuum platinum-rhodinm^ or 

 platiuum platinnm-iridium éléments^ correspondhig to any desired 

 température up to the melting point of that métal, This metliod pos- 

 sesses the advantage of extrême simplicity and it affords indications the 

 accuracy of which leaves little to be desired. 



The acétylène flame employed in this method of calibration is of the 

 usual flat form produced by the union of two impinging jets. There are 

 three distinct stages observable in the form of such a flame, depending 



') SuîMENS W. Proc. of Ihe Royal Sociehj (Loiidon) XIX, p. 351. (1871) also 

 Reports of tiie BrilisJi Association. (1874) \). 242. 



') Callendar; Philos. Trans. (1888) p. 160; (1892) p. 119; also Philos. Macj. 

 XXXII, p. 104, (1891); XXXIII, p. 220 (1892). 



'') Violle; Comptes Rendus, LXXXV, 543; LXXXIX, p. 702. 



") NiCHOLS; Physical Review, X, p. 234 (1900). 



