One of the country's top digital humanists has been tapped to lead one of an ambitious effort to create a national home for the country's digital riches. The Digital Public Library of America, an effort to "make the cultural and scientific record available to all," announced the hiring Tuesday of Dan Cohen, director of the Roy Rosenzweig Center for History and New Media and an associate professor in the Department of History and Art History at George Mason University, as its founding director. The digital public library, which in its nascent form has been housed in Harvard University's Berkman Center for Internet & Society, will formally launch as a freestanding nonprofit entity on April 18.