. Instrumente und Methoden in der Radiometrie verwendet, III - die photoelektrische Zelle und andere selektive Radiometer . 38 Kupferlackdraht. 3 Dieses Bulletin, 7, S. 245, 1911; 13, S. 358 und 360, 1916. 5 20 Bulletin of the Bureau of Standards [Vol. 14 Erdung. Bei Verwendung der hochohmige Spulen würde jedoch die höchste Stromempfindlichkeit eine Erdung des Geräts erfordern. (G) der Hilfselektrometer. – der Elektrometer, der am häufigsten verwendet wird Wth eine photoelektrische Zelle ist das Dolezalek ^^ Instrument;Miillys Elektrometer ^- wurde auch verwendet. Ein neuer Quadrant Elec-Trometer von Compton ähnlich dem
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. Instruments and methods used in radiometry, III - The photoelectric cell and other selective radiometers . 38 enameled copper wire. 3 This Bulletin, 7, p. 245, 1911; 13, pp. 358 and 360, 1916. 5 20 Bulletin of the Bureau of Standards [Vol. 14 grounding. However, when using the high-resistance coils thehighest current sensitiity would necessitate grounding theinstrument. (g) The Auxiliary Electrometer.—The electrometer most com-monly used Wth a photoelectric cell is the Dolezalek ^^ instrument;Miillys electrometer ^- has also been used. A new quadrant elec-trometer by Compton similar to the Dolezalek instrument is justappearing on the market.^ In order to shield the electrometer from leakage, static charges, etc., the whole apparatus including the photoelectric cell, isusually inclosed in a tight metal box and the moisture is absorbedby drying material; for example, calcium chloride or better stillphosphorus pentoxide. The metal box is grounded. The needle is usually charged to a potential of 80 to 100 volts.^*One pair of quadrants is grounded. The other pair of quadrants, (^^^-> ^:rL. W-ihl G-roand Gt. Fig. 6.—Arrangement of apparatus used by Nathan^on which can also be grounded, is connected to the cathode of thephotoelectric cell. Nathonson ^^ haing the electrometer and the photoelectriccell in separate boxes found it necessary to protect the connectingwires. Fig. 6, between these two instruments by passing themthrough a glass tube which was covered with tin foil and was wellgrounded. To overcome the drift of the needle of the electrometer *i Made by the Cambridge Sci. Inst. Co., Cambridge, England; Dolezalek, Z. S. fiir Instrimxentenkiinde21, p. 345. 1901. «Mully, Phys. Zeitsch., 14, p. 237; 1913. ** Compton, Phys. Rev. (2), 7, p. 646; 1916. Made by the PiToelectric Instrument Co., Trenton, X. J. ^ The quartz-fiber suspension is from 6 to 9 m thick; giving a free period of swing of 15 to 20 seconds, anda sensitivity of 300 to 3000 mm per volt differen
