I was looking at 1815: The End and a Beginning by John Fisher for another reason, and came across the following:
"In April, Sir Humphrey Davy, already famous for the discovery of new elements such as dedededum dedum, returned to England. Even then scientists regarded themselves as above politics and Davy, after being awarded a scholarship by Napoleon for his researches into explosives, had been touring the Continent with his assistant Michael Faraday on a laissez-passer from the Emperor himself ... " (from the work cited above, page 114.)
When I read it, I remembered I had read this before, long long time past.
That was part of the reason Grey pretends to be a German Professor of Physics when he's stopped by the gendarmes near the coast. ... Because Napoleon was in the habit of giving free passage to scientists to travel from place to place. The 1815 book is one of the refs to it.
Here's one of those examples of how background reading wanders into what we write. I couldn't have put my finger on all the thirty or fifty times I'd come across refs about Napoleon giving free passage to scientists. I didn't consciously think ... 'Grey will pretend to be a scientist because of yada yada from this particular book.'
But it was inside me when I needed it.