by the appearance of the hydrogen lines. In later experiments Ramsay and Collie37 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. |
The experiments were repeated with a new supply of emanation, and some of the stronger lines were observed again, while some new lines made their appearance. Ramsay and Collie suggest that the strong line 5595 may be identical with a line which was observed by Pickering38 in the spectrum of lightning, and was not identified with the spectrum of any known gas.
Until large quantities of radium are available for the experimenter it would appear difficult to make sure how many of these lines must be ascribed to the spectrum of the emanation or to measure the wave-lengths with accuracy.