In his short treatise, Sidereas nuncius (Starry Messenger, 1610), Galileo Galilei presented his lunar observations, recording what he saw by projecting the image of the moon through a telescope onto a piece of paper and tracing this image with a sepia ink. Prevailing theories accounting for the variety of light and dark areas of the moon held that the moon was either a gaseous or a reflective orb. With an enhanced visual capacity and his knowledge of chiaroscuro, Galileo surmised that the surface of the moon was akin to the surface of the earth with shadows cast by mountain ridges into the valleys below. A few years later in Istorie e dimonstrazione (Histories and Demonstrations, 1613), Galileo elaborated on confronting doubt and truth:
I do not possess such a perfect faculty of discrimination. I am more like the monkey who firmly believed that he saw another monkey in the mirror… and discovered his error only after running behind the glass several times… I should like to know the visual differences by which he [his adversary] so readily distinguishes the real from the spurious.