1904.] 



The Spectrum of the Radium Emanation. 



475 



of the disintegration of the emanation. This, however, is very 

 doubtful, and judgment must be suspended until more satisfactory 

 evidence is forthcoming. 

 The lines read were : — 



Wave-length. Remarks. 



6350 Not observed before ; faint. 



5975 Observed before ; faint. 

 5955 



5890 Not observed before ; faint. 

 5854 



5725 Observed before ; fairly strong. 



5686 Not observed before ; faint. 



5595 Observed before; strong and persistent. 



5580 Not observed before ; faint. 



5430 



5393 ,, ,, 



5105 Bright; persistent; observed before. 

 4985 ,, ,, ,, 



. 4966 Not observed before ; bright, but transitory. 



4640 Transitory; possibly 4650 and 4630, which were 

 seen before as distinct lines. 



The line 4966 was particularly brilliant at first; but it soon assumed 

 secondary importance. Some lines which had previously been observed 

 were not seen; they are 6307, 5805, 5137, and 4690. An attempt 

 was made to obtain the spectrum with a jar and spark-gap; but only 

 hydrogen and mercury were to be seen. The resistance soon became 

 very high, and there was danger of piercing the vacuum-tube. 



Previous attempts in conjunction with Mr. Soddy gave lines with 

 wave-length 5725 (jar), 5595 (no jar), 5105 (no jar), 4985 (no jar); the 

 line 5585 was observed three times, and 5105 twice previously. The 

 lines 6145 and 5675 mentioned in our last paper (April, 1904) were 

 not seen, unless the latter is identical with 5580. It may perhaps 

 be mentioned that the line 5595 was seen by Pickering in the 

 spectrum of lightning, and was not identified with a line in the spectrum 

 of any known gas ; it is said to have been a very strong line, of 

 intensity 30.* 



There can be no doubt that the lines given are the chief lines in the 

 visible spectrum of the emanation ; as for the pressure, the volume of 

 emanation was about l/30,000th of a cubic centimetre, and the capacity 

 of the vacuum-tube, say, l/20th; this would make the pressure about 

 l/10th of a millimetre. It may have been twice as much, for the 

 numbers given are merely estimates. 



It may be remembered that, at the Chemical Congress held in Paris 



* ' Astrophysical Journal,' 1901, vol. 14, p. 368. 



