Fiona Ritchie, the founder, producer, and host of National Public Radio’s The Thistle & Shamrock®; and Doug Orr, who has led and UNC-Asheville and Warren Wilson College, where he founded the Swannanoa Gathering music workshops are the authors of “Wayfaring Strangers: The Musical Voyage from Scotland and Ulster to Appalachia” and talk about the 300-year story of that musical migration.