 In the Dialogue, things are more complicated than we have just sketched. Galileo, as noted, argues for circular natural motion. Yet he also introduces, in places, an intrinsic tendency for rectilinear motion. For example, Galileo recognizes that a stone whirled circularly in a sling would fly off along the rectilinear tangent if released (Galilei 1967, 189–94; see Hooper 1998). Further, in Day Four, when he is giving his mechanical explanation of the tides, he nuances his matter theory by attributing to water an additional power of retaining an impetus for motion such that it can generate a reciprocal movement once it is sloshed against a side of a basin. This was not Galileo’s first dealing with water. We saw it first in the De Motu around 1590, where Galileo discusses submerged and floating bodies, but he learned much more in his dispute over floating bodies (which produced the Discourse on Floating Bodies in 1612). In fact, a large part of that debate turned on the exact nature of water as matter, and what kind of mathematical proportionality could be used to correctly describe it and bodies moving in it (see Palmieri 1998; 2004).