Conversation so far:
What were Alexander Graham Bell's later inventions?
Alexander Graham Bell's later inventions included 14 for the telephone and telegraph, four for the photophone, one for the phonograph, five for aerial vehicles, four for hydroairplanes, and two for selenium cells.

Question: What ideas did he have regarding teaching speech to the deaf?
Self-contained rewrite: What ideas did Alexander Graham Bell have regarding teaching speech to the deaf?