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 and temperature, and that the emanation was produced from 1 gram of radium at the rate of 3 × 10^{-6} c. mm. per second. This amount is in very good agreement with the calculated value, and is a strong indication of the general correctness of the theory on which the calculations are based.

173. Spectrum of the emanation. After the separation of the emanation and the determination of its volume, Ramsay and Soddy made numerous attempts to obtain its spectrum. In some of the earlier experiments several bright lines were seen for a short time, but these lines were soon masked by the appearance of the hydrogen lines. In later experiments Ramsay and Collie succeeded in obtaining a spectrum of the emanation, which persisted for a short time, during which a rapid determination of the wave-lengths was made. They state that the spectrum was very brilliant, consisting of very bright lines, the spaces between being perfectly dark. The spectrum bore a striking resemblance in general character to the spectrum of the gases of the argon family.

The spectrum soon faded, and the spectrum of hydrogen began to appear. The following table shows the wave-length of the lines observed in the spectrum. The degree of coincidence of the lines of known wave-lengths shows that the error is probably less than five Ångström units.

Wave-length                    Remarks 6567    Hydrogen C; true wave-length, 6563; observed each time. 6307    Observed only at first; evanescent. 5975       "              "          "   5955        "              "          "   5805     Observed each time; persistent. 5790    Mercury; true wave-length, 5790. 5768       "             "         5769.   5725     Observed only at first; evanescent. 5595    Observed each time; persistent and strong. 5465    Mercury; true wave-length, 5461. 5105    Not observed at first; appeared after some seconds; persisted and was visible during the second examination. 4985    Observed each time; persistent and strong. 4865    Hydrogen F; true wave-length, 4861. 4690    Observed only at first. 4650    Not observed when the emanation was examined again. 4630          "               "                "   4360     Mercury: true wave-length, 4359.