"They have become very popular and widespread in my time. You should be proud." It's decided. He's not going to tell Watson the truth and steal that pride from him. What would it help?

"Mm. Yes, I...well, having read what you wrote on that subject I can see why."

Right. Perhaps a new topic? "I wonder, Dr. Watson, would you happen to have a kettle? I know it's not quite the right hour yet, but I could do with a cup. If I could be so bold as to impose?" When in doubt, tea.