In a book soon to be published, Lester says Leonardo used to travel with a small notebook hanging from his belt, and “whenever something caught his eye,” he would make a note, or begin “sketching furiously.”

“It is useful,” Leonardo wrote, to “constantly observe, note, and consider.” But when you are Leonardo, what sorts of things are buzzing around in your head? Well, Toby Lester describes what is essentially a “To Do” list buried in one of those notebooks, a bunch of things Leonardo planned to do one week, or month, in the early 1490’s. (via)