Photo-chemistry / by S.E. Sheppard.

  • Samuel Edward Sheppard
Date:
1914
Catalogue details

Licence: In copyright

Credit: Photo-chemistry / by S.E. Sheppard. Source: Wellcome Collection.

    72/484 page 56
    necessary above 2000°,1 so that radiations can be compared both with standard “ black ” radiation and with each other. § 24. The Radiation Function. Kirchhoff himself stated that full value of his law would only be obtained when the form of the function could be experimentally found which was determining the radiation of the black body for every wave-length and every temperature. For pure temperature radiation, this law puts the emission of all bodies in simple relation to that of the black body. Fa We have expressed this law in the form = SA, which gives us, when Aa = 1, SA = EA. The function SA expresses the most general form possible of the relation of radiation to temperature and wave-length; it is the general radiation func- tion, independent of the specific absorptive properties of individual substances. It gives at the same time the highest value which the radiation of a body can attain for a given temperature. But it must be borne in mind that we are only concerned with pure temperature radiation. How far thermo- dynamic considerations can be applied to the emission of light when this is due, in part or entirely, to chemical changes, will be discussed later.:: § 25. The Stefan-Bolzmann Law. The law relating the total radiation S of the black body to its temperature was empirically deduced by Stefan 4 from 1 By the use of iridium as the material, W. Nernst, Phys. Zeitschr., 4, 733 Owl- 2 The methods and instruments (bolometers, radiometers, radiomiero- meters, etc.), for the measurement of radiation qua heat will be found discussed in Spectroscopy, E. C. C. Baly ; K. Schaum, Photochemie ami P/iotog., Pt. I., p. 16. See also reports of the Physical Technical Reichs- anstalt in recent years, Zeitschr. f. lust. Kuvde and Zeit. miss. Phot., 1900-1910. See Chapter VII. 1 Silz. Ber. Wiener Akad., 79, Abt. II. 391 (1S79).
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