. Strumenti e metodi utilizzati nella radiometria, III - la fotocellula e altri radiometri selettivi. F conducibilità elettrica ampiamente diversa. L'assenza di polarizzazione indica che la conduzione non è elettrolitica. Gli esperimenti a temperature liquido-aria, dove viene mantenuta la sensibilità all'altezza, sembrano essere prove a sostegno dell'ipotesi elettronica.^^ in conclusione si può aggiungere che la cellula di selenio può essere utilizzata come indicatore nei metodi di null e di eguale deflessione di ottenere rapporti di intensità che sono stati considerati nel Pfund. Fisiol. Rev., 34, pag. 370; 191:. Stcbbi

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. Instruments and methods used in radiometry, III - The photoelectric cell and other selective radiometers . f widely different electrical conductivity.The absence of polarization indicates that the conduction is notelectrolytic. Experiments at liquid-air temperatures, where thelight sensitivity is retained, seem to be evidence supporting theelectronic hypothesis.^^ In conclusion it may be added that the selenium cell may beused as an indicator in the null and the equal-deflection methodsof obtaining ratios of intensities which were considered in the Pfund. Phys. Rev., 34, p. 370; 191:. Stcbbins, Astrophys. Jour., 39, p. 459, 1914; 4*2, p. 133, 1915. <* Stebbins, Obseratory, No. 501, p. 257; 1916. M Elliot, Phys. Rev. (2), 5, p. 33; 1915. Cobleniz] Selective Radiometers 529 operation of the photoelectric cell. For example, the galvano-meter deflection might be observed when the cell is exposed for, say, five seconds to the lower intensity. Then the higher intensityis reduced, by means of (calibrated) crossed Nicol prisms, a wiregrating, an absorption wedge, a variable-sector disk, or some. sg^ Fig. 8.—Distribution of energy in the spectrum of a Nernst gloiver as observed with anonselective radiometer, A, and with a selenium cell, B. Curves C and D (from Pfund)give the responses of a selenium cell in an equal energy sptcirum Other device, to give the same deflection. In this manner theratios of intensities of monochromatic light of the same wavelength might be observed; but the selenium cell can not be usedin this manner to compare accurately the intensities of light oftwo sources differing in color. This restriction applies, of comse, to all of the instruments discussed in this paper. 530 Bulletin oj the Bureau of Standards [Vd. 14 IV. PHOTOGRAPHIC RADIOMETRY The use of the photographic plate is a roundabout method formaking radiometric measurements. It has been used in meas-uring the distribution of energy in the spectrum of the light ofthe firefly, ** and, more

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• bookauthorcoblentz
• bookcentury1900
• bookdecade1910
• bookyear1919