I want to know the answer to the following question:
What series of books does Gray say Bell would go to sleep reading?
All the background I'm provided with is that "According to one of his biographers, Charlotte Gray, Bell's work ranged "unfettered across the scientific landscape" and he often went to bed voraciously reading the Encyclopædia Britannica, scouring it for new areas of interest.". Is that enough to answer the question?