Published in 1613, Galileo Galilei's Istoria e dimostrazioni intorno alle macchie solari e loro accidenti (Account and demonstrations concerning sunspots and their origins), contained letters by Galileo on sunspots. By including illustrations of his observations on the same page as the text, he was able to refer to a particular spot (e.g. "La macchia A.") and the date on which he observed it. The portrait of Galileo (above) was included at the front of the book.