Lamya Kaddor teaches Islamic studies in Germany. She's written a new book, Zum Toeten Bereit (Ready To Kill), about the experience of having five former students flee to Syria to join jihadist groups. Andre Zelck/Courtesy of Piper Verlag GmbH hide caption

itoggle caption Andre Zelck/Courtesy of Piper Verlag GmbH

The empty frame from which thieves cut Rembrandt's The Storm on the Sea of Galilee remains on display at the Isabella Stewart Gardner Museum in Boston. The painting was one of 13 works stolen from the museum in 1990. Josh Reynolds/AP hide caption

itoggle caption Josh Reynolds/AP

Benjamin Rush, a physician and one of the signers of the Declaration of Independence, invented the rotational chair as a treatment for psychotic patients. He believed the chair helped improve circulation to the mentally ill brain. U.S. National Library of Medicine/Courtesy of Little Brown and Company hide caption

itoggle caption U.S. National Library of Medicine/Courtesy of Little Brown and Company