1903.] Spectrum of tlic Spontaneous Radiation of Radium. 409 



"Further Observations on the Spectrum of the Spontaneous 

 Luminous Eadiation of Radium at Ordinary Temperatures." 

 By Sir WILLIAM HUGGINS, K.C.B., O.M., D.C.L., Pres. R.S., 

 and Lady HUGGINS, Hon. Mem. R.A.S. Eeeeived October 29, 



1903. 



[PLATE 19.] 



In the plate accompanying our paper on the spectrum of the glow 

 of radium bromide,* at least seven lines are seen to agree, both in 

 position and in intensity, with corresponding lines in the band spectrum 

 of nitrogen. We called attention to other lines, of which some traces 

 may be detected on the plate, and we suggested that with a longer 

 exposure a more complete spectrum would be obtained. One strong 

 line in the radium bromide glow spectrum, about 3914, has no similar 

 line corresponding to it in the band spectrum of nitrogen as given on 

 the plate. 



We have since taken photographs, with longer exposures, of two 

 specimens of radium bromide, one prepared by Buchler and Co., and 

 the other received from the Societe Centrale de Produits Chimiques. 

 In these photographs, lines only faintly glimpsed in our earlier 

 photographs can be seen distinctly. A photograph taken of the French 

 radium bromide with an exposure of 216 hours, is reproduced on the 

 accompanying plate. 



The coincidence of the spectrum with the band spectrum of nitrogen 

 is shown to be even more complete by the presence of a faint trace of 

 the next more refrangible band, beginning at 2976*7. In addition, 

 some of the fainter single lines of the nitrogen spectrum now come out 

 in the radium bromide spectrum. 



At the same time that the coincidence down to minuter details with 

 the nitrogen band spectrum is brought out, the strong outstanding 

 line, about 3914, is now seen to be accompanied by a second, but less 

 intense, outstanding line at about 4280 ; neither of which is present in 

 the ordinary band spectrum of nitrogen, which was the one reproduced 

 on the plate of our first paper. 



This nitrogen band spectrum is the one distinguished by Deslandres 

 as that of the positive pole, but it appears at all parts of a vacuum 

 tube, and is also produced when a suitable induction coil discharge, 

 without capacity, is taken across air at the ordinary density. The 

 nitrogen spectrum that was measured by Ames was taken by using an 

 end-on vacuum tube closed with a quartz plate ; in his list no lines are 

 given at the places of the two outstanding lines in the glow spectrum. 



When, however, the spectrum is taken of the aureole about the 



* ' Roy. Soc. Proc.,' vol. 72, p. 196. 



