Jean Ritchie, who performs tonight at Georgetown University's Gaston Hall, is one of the finest traditional singers in America. She also happens to be the great popularizer of the mountain dulcimer, which the Viper, Ky., native first took on the road during the early '40s.

"I'm proud of that," she says of her missionary work. "It was thought of as a quaint instrument from the Appalachians. The only other people who played it were John Jacob Niles and Andrew Rowan Summers of Virginia. Niles tried to keep it a mystery and would never talk to people about the instrument. I told people that anybody could play it, that it was a by-ear instrument. Of course, there were no rules for people to follow and a lot of people had trouble with that."

Ritchie, who is also a fine songwriter and collector of folk songs, helped break the ice by writing a number of instruction books and recording numerous albums that influenced later popularizers like Richard Farina and Joni Mitchell. These days, dulcimer makers have their hands full meeting the demand for that most social and simple instrument. Ritchie, on the other hand, hardly has enough room in her home for the 50 dulcimers she now owns. "There piled up in closets, all over," she says. "People just send them to me.