The Codex Leicester, later renamed the Codex Hammer, was one of da Vinci's many scientific journals. It was published in 1510 and its contence mainly focused on his ideas on water and the moon.  An interesting note about this text is the "mirror image" style it is written in, meaning that it should be read from right to left, appearing normally in its reflection.  The Codex als holds the record for the second largest price tag, purchased by Bill Gates in 1994 for $30.8 million dollars, making the manuscript also the only of da Vinci's journals to be privatly owned.