358 Transactions of the Boyal Society of South Africa. 
tubes were occasionally turned over, so as to spread the colouration over 
as large a surface as possible. 
Fig. 1. 
M = 1-1 Diameters. 
On making a close examination of these tubes a marked difference 
was seen in the manner in which the colouration had developed in the 
two kinds of glass ; the photographs show this difference very clearly. 
Fig. 2. 
M = 1-5 Diameters. 
Pieces of the radium-coloured tube and of the control sample were cut 
off, the ends ground and roughly polished, cover glasses being placed over 
