400 Sir W. Crookes. 



the buttons faced round, always presenting the blue face to the- 

 negative pole. Examination with a spectroscope showed strong 

 hydrogen lines in the pink parts, and both hydrogen and mercury in 

 the blue parts. Fig. 1 shows the appearance at this stage. 



Pio. 1. 



The exhaustion was now raised to 2 mm., when the whole of the 

 blue faces of the parti-coloured buttons suddenly migrated to one 

 bright blue, Avell-formed button, nearest the negative pole, all the 

 other buttons remaining pink. The appearance is shown in fig. 2. 



FIG. 2. 



Round the negative pole an indistinct halo showed both mercury and 

 hydrogen ; but on the blue button mercury only was detected, not 

 a trace of even the brightest hydrogen line being there seen. On the 

 pink portions the hydrogen lines were in excess, but mercury could 

 be seen all along the tube.* 



* I hare been unable to find any reference to this concentration of the blue 

 constituents of the strata into one single button at the end near the negative pole. 

 In the classical researches of Messrs. De la Hue and H. W. Mliller on the 'Electric 

 Discharge with the Chloride of Silver Battery,' numerous references are made to 

 the blue and pink parti-coloured character of the strata, and also to the change of 

 colour from all blue to all pink which follows a change in the electrical condition?. 

 Thus we read : " Thirty-nine strata, the convex side being blue and the broader 

 concave side reddish." " Twenty-one strata, very blue on the convex face, pink on 

 the concave." ' Phil. Trans.,' vol. 169, p. 175. 



Sometimes the stratifications are described as all of one colour : " Twenty-one 

 very blue strata." " The strata were blue, and sixty-one in number." " Showing 



