46 ILLINOIS ACADEMY OF SCIENCE. 



spectrum of this faint lig'ht, which you now see upon the screen. 



As you observe it is practically identical with the banded spec- 

 trum of nitrogen as seen about the negative pole, the cathode of a 

 vacuum tube. 



The natural inference, that this spectrum is due to the cathode. 

 that is, to the p rays which radium emits, has been disproved; 

 not only so, but it has been shown that when radium is placed in 

 an atmosphere of hydrogen it does not yield the hydrogen spec- 

 trum, but continues to give that of nitrogen. 



Indeed, the origin of this nitrogen spectrum is, so far as the 

 speaker is aware, an unsolved problem. It is a spectrum of very 

 considerable interest, as pointed out by Sir William Huggins, 

 because it is the only known case in which the ultraviolet lines 

 of a gas have been obtained without the use of an electric 

 discharge. 



Dr. Gordon Fulcher of the University of Wisconsin is now 

 preparing to examine the effect of bombarding a fine capillary 

 jet of air with a stream of canal rays. It will be interesting to 

 learn whether he obtains, in this manner, the same luminosity as 

 that produced by radium in the air immediately surrounding it. 

 If he does, it would seem at least probable that this nitrogen 

 spectrum is due, not to the /S but the a rays of radium. 



SPECTRUM OF RADIUM EMANATION. 



But radium has many ways of affecting the "outside world." 

 Beside its well known a, (3, and y radiation, its arc, spark and 

 flame spectra, and its self-luminosity, any one of which is suffi- 

 cient to confer distinction upon an element, it gives off a heavy 

 gas which Rutherford first called an emanation — and which is 

 transported through the surrounding air, ionizes the air, and 

 finally disintegrates into a solid, called the active deposit, at such 

 a rate that in four days the activity of the gas has diminished to 

 one-half. Rutherford and Royds* have taken great pains in pre- 

 paring a spectrum-tube of very pure radium-emanation, and they 

 find that the heavy inert gas has a characteristic bright line 

 spectrum of its own, quite different from that of radium and 

 quite similar to that of Helium, Neon, Argon and Krypton. 



In 1903 Ramsay and Soddy went one step further; they pre- 

 pared a spectrum tube, filled it with radium emanation, condensed 

 it in a side tube in liquid-air so as to avoid getting any helium 



^Rutherford and Royds Phil. Mag. 16, 313 (1908). 



