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The In tern atio n al Tem perature Scale, which has been in force since 1927* is based on certain values assigned to th e boiling and freezing points of pure substances and on specified m eans of interpolation between, or extrapolation beyond, these points. The highest basic p oint of th e scale is the freezing point of gold, defined as 1063 • 0° C, while for extrapolation from this tempera tu re use is m ade of th e W ien law of radiation, w ith a certain value of the constant C2. Though any tem peratu re above 1063° C is thus completely defined w ithout reference to fu rth er fixed points, determinations of such points are of considerable value. I n particular, th ey serve to indicate the degree of reproducibility of th e scale by th e various users of it, and, when well authenticated, to provide secondary standards for its realization. Of such fixed points th e m ost im p o rtan t has been th e freezing point of palladium (1555° C), b u t th e latest developm ents in furnace technique and refractory m aterials should now enable th e freezing point of platinum to be used with equal, if n o t greater, advantage. The qualities of platinum which render it especially valuable in this connection are as follows : its freedom from oxida tio n ; its high stan d ard of purity, for which a convenient electrical test is available ; its high freezing point (about 1775° C) which approaches the im p o rtan t zone of tem perature covered by th e electric fighting industry These qualities also m ake th e platinum point especially suitable as the basis for a standard of fight, as has been proposed by a num ber of experimenters.I t is w ith th e tw o objects indicated above th a t the National Physical Labes* to ry has undertaken an investigation concerning th e freezing point of plaWpP* th e precise scope of which m ay be defined as follows :- on May 11, 2018 http://rspa.royalsocietypublishing.org/ Downloaded from

* 4 Comptes rendus des Seances, Sept. Conference generale des poids et mesures,' Paris, 1927. t The scale is actually defined by the assignment of certain values to the melting or boiling points of a number of pure substances, and bj^ prescribed means of interpolation between these temperatures, the whole being based on work with the gas thermometer. % The definition adopts the Wien law as confined to monochromatic visible radiation. When thus limited the two laws become practically identical.

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The relation between the thermal and electrical conductivities of metalslA has for a long time engaged the attention of physicists. As far back as 18535 Wiedemann and Franz* propounded the law to the effect that the ratio of the* two conductivities was the same for all metals. In 1872 Lorenzf, both on theo-x retical and experimental grounds, sought to establish that the above-mentioned*9 ratio was proportional to the absolute temperature. On the development of > the electron theory Drude, H. A. Lorentz, J. J. Thomson and othersj have,a| on the basis of various assumptions, arrived at the same conclusion as Lorenz, i Up to 1900, however, the experimental values were too uncertain to allow any c definite confirmation of the theory. In that year Jaeger and Diesselhorst § % published the result of their investigation, which gave directly the ratio of the a conductivities for a number of metals and alloys over the range 18° to 100° C. I Lees|| has since, by an independent method, confirmed the values of Jaeger and i Diesselhorst for a number of metals at 18° C. and has carried the investigation x * * * §