In the early 17th century the modern version of the Duhem–Quine thesis had not been formulated, but common sense objections to such elaborate and ad hoc implicit auxiliary assumptions were urged. To begin with, the mechanism of the (Galilean) telescopes had been explained in terms of geometrical optics and the nature of the objects that they imaged was consistent; for example a distant lake would not resemble a tree when seen through a telescope. The behaviour of telescopes on Earth denied any basis for arguing that they could create systematic artefacts in the sky, such as apparent satellites that behaved in the predictable manner of Jovian moons. Evidence also offered no basis to suggest that they could present yet other, more elaborate artefacts, fundamentally different from the satellites, such as Lunar mountains that cast shadows varying consistently with the direction of Solar illumination.