Democritus Junior to the Reader, page 16

[p. 16]
My intent is no otherwise to use his name than Mercurius Gallobelgicus, Mercurius Britannicus, use the name of Mercury, Democritus Christians,* etc.;...

* R.B.: Auth. Pet. Besseo, edit. Coloniæ, 1616.

Mercurius was a brand of newspapers, or more properly, news books. The idea was copied after the Mercure française, launched in France in 1611. First to appear was the Mercurius  Britannicus, which in 1625 became the first English news periodical to carry that title.
(from Jonathon Green, The Vulgar Tongue: Green's History of Slang, Oxford University Press, 2011, p. 100)

The dates would seem to suggest that this name was thrown in in a later edition (Burton was a notorious re-writer).