Hereaus gave in the hands of the present writer .U1S2C volts at the sauie temperature. Siemens ') and later, Gallendab 2), and his coworkers have shown the same to be true in platiiium thermometry.
To tliis end, nunierons more or less complicated methods involving the use of various forins of the gas thermometer have been proposed, the carrying out of which involves the use of special apparatus which is difticult of construction and so laborious in operation, as in many cases to involve a far greatcr expenditure of time than is necessary for the investigation in which the thermo-elements are to be eniployed. By means of sucli apparatus in tlie hands ot' the investigators already mentioned, and by tlie independent methods eniployed by Yioi.i.e !), the melting points of eopper, silver, gold, palladium, and platiiium have been observed witli a fairly satisfactory degree of aecuracy; so that we are now in position lo use tliese melting temperatures as reference jioints upon a calibration scale. Wide dillerences of opinion slill exist concerning tlie absolute values to be assigned to them, but a provisional scale of temperatures al least may tlius be established for any thermoeleinent for which the electroniotive forces produced when tlie hot junction is brought to the temperature of tliese metals at tlieir points of fusion can be determined.
Tn the course of a recent series of studies !) 011 tlie acetylene tlanie, L have shown that tliis source of radiation possesses a temperature above tlie melting point of platiiium and that it may be used for tlie determination of the electroniotive forces of platiiium platinmii-rhodiuin, or platinum platinum-iridium elements, corresponding to any desired temperature up to the melting point of that nietal. 'Tliis niethod possesses the advautage of extreme siniplicity and it affords indicatious the aecuracy of which leaves little to be desired.
'Tlie acetylene tlame eniployed in tliis niethod of calibration is of the usual flat form produced by the union of two impiuging jets. 'Tliere are three distinct stages observable in the form of sucli a flaine, depending
') Sikheks W. Proc. of llie Royal Society (London) XIX, p. 351. (1871) also lieports of Ihe Brilish Association. [ 1874) p. 242.
') Cali.i ndar; PI,Hos. Trans. (1888) p. 160; (1892) p. 119; also Philos. Maj. XXXII, p. 104, (1891); XXXIII, p. 220 (1892).
3) Violle; Comptes Kenilus, LXXXV, 543; LXXXIX, p. 702.
') Niciioi.s; Plii/sical llevieic, X, p. 234 (1900).