1903.] Correction to Paper ly Sir W. Crookes. 413 



graphs, taken with the spectroscope in different positions, failed to 

 show the smallest trace of shift from flexure. The only suggestion 

 we can make in explanation is that the piece of solid radium 

 bromide accidentally shifted in its cell, so as no longer to be directly 

 under the slit, and in consequence the collimator lens was not wholly 

 filled with light. 



The results of the experiments described in this paper would appear 

 to show generally, if analogy with electric stimulation may be assumed, 

 that the radium stimulation, whether we take the operative cause to 

 lie in the j3 rays, or in the encounters of nitrogen molecules with the 

 active molecules of radium by which, for the first time, a spectrum 

 of bright bands in the ultra-violet region has been obtained at 

 ordinary temperatures, and without the intervention of an electric 

 discharge from the very circumstance of its being of such a nature 

 as to give rise to the band spectrum of nitrogen, is not of a kind which 

 can elicit from either the molecules of bromine, or of radium their 

 characteristic line spectra. 



The question suggests itself whether or not the same inability may 

 hold in respect of the helium molecule, which is easily stimulated jby 

 an electric discharge ; we have not as yet made experiments on this 

 point. 



" Correction to Paper ' On the Spectrum of Kadium.' " By 

 Sir W. CROOKES, F.RS. Received November 9, 1903. 



The faint line 3961-624, described* as a radium line, is due to 

 aluminium, being one of the strongest lines in the Al spectrum. Its 

 wave-length, recently measured on a special aluminium photograph, 

 shows the identity ; moreover, with a pure salt of radium it is found 

 to be absent. 



* ' Koj. Soc. Proc.,' this volume, p. 300. 



VOL. LXXII. 2 CT 



