After experiencing severe famine in Malawi in 2001, William Kamkwamba wanted to find a way to protect his family in the future. So he set out to build a windmill, using diagrams from an old physics textbook and scrap parts that he collected in the local junkyard. Host Jeff Young talks with William Kamkwamba and journalist Bryan Mealer, co-authors of “The Boy Who Harnessed the Wind.”