Admirers of Jean-Jacques Rousseau may be unaware of his musical interests.  He wrote a great deal of music, compiled a musical dictionary, and paid bills by copying music.  The dictionary is a neglected treasure, as passionate and eccentric as anything else he wrote; the entry for “copyist” fills 13 pages (at least in the 1839 edition that beckons on my shelf).  Here’s an excerpt (as usual, in my translation):

“It is more important for music to be copied neatly and correctly than it is for simple writing, because he who reads and meditates in his chamber can easily recognize and correct errors in his book, and because nothing prevents him from stopping or beginning again: but in a concert, where each player sees only his own part, and where the speed and flow of the execution leave no time for correction, mistakes are irreparable: often a sublime piece of music is crippled, the performance interrupted or even halted, everything goes wrong, the ensemble and effect are ruined, the listener is rebuffed, and the composer dishonored, all because of the copyist.”

(Posted by Doug Skinner.  The music above was copied by Rousseau in 1773.)