I popped into the local library yesterday to ask them to borrow the relevant magazine for me. Unfortunately, it's their view that the BL will not lend them magazines, only supply an expensive photocopy if I can give them the article title and page number(s). These I don't have.
The only reference is in an article photocopied from the January 1931 issue in the article "The Penrhyn Slate Quarries" which states that there is an article on Fullersite "elsewhere in this issue".
Looks like I'll have to give my freedom pass some exercise and go up to St Pancras.
Penrhynman.