Possible Clues:

• Loss through emigration
• Drift of stuff that is grey or black, leading to repeated precipitation around break of day
• Migration of highly trained people
• Intellectual exodus
• Exodus of intellectual talent
• Result of a professor's departure?
• Loss of people's ability to benefit others
• Grey matter going across the pond?
• Minds leaving the country
• Bishop died during lots of bad weather, such a loss of talent