WHEN writing my communication published in Nature of August 5, I had to rely on abstracts of Mr. Schulman's papers; this was responsible for my misrepresentation of Mr. Schulman's point of view. The information now supplied by Mr. Schulman is very interesting, for it appears that none of the bands observed in my system is present in the silver-free base studied by Schulman, and his 420-mµ band is completely absent in my system. This shows that a more critical study of this system is necessary before these bands can be assigned definitely to various trapping centres, although I have made some tentative assignment from the study of glass systems of different composition.