Bill Gates bought the Codex Leicester a notebook of Leonardo da Vinci's scientific observations and theories in 1994 from the estate of Armand Hammer for $30. 8 million. Last year Gates loaned the work to Australia's Powerhouse Museum, which prepared this companion to its exhibition. No longer in codex form (the pages were bound in the 1600s, but Gates had the binding dismantled for digital reproduction), the manuscript ranges over topics from fossils to astronomy. Each recto of this edition reproduces one of Leonardo's pages, written in mirror-script Italian with sketches jotted in the margins; a discussion (but not a translation) appears on the verso. It includes an introduction to Leonardo's life, but no index.