Nicholas of Cusa (c.1400-1464) believed in using reason to determine how the universe worked. He did not exactly take a "scientific" approach: he argued from his understanding of metaphysics and, in some cases, numerology. His guesses, however, were better than some early scholars' observations.
Because he could not accept that God was finite, and since God is not separate from the entirety of the universe, he argued that the universe must by necessity be infinite. Also, because God must provide the center for His own totality, the Earth cannot be at the center of the universe—that would mean Earth was the center of God. Not being at the center of the universe, the Earth cannot be immovable, and it, along with the Sun, must be in motion just like every other observable heavenly body. This idea influenced Giordano Bruno.
Again, denying perfection for anything but God, he would not accept planetary orbits as perfectly circular, paving the way for Kepler (who referred to Nicholas as "divinely inspired") to design elliptical orbits in his planetary theory.
Cusa's thoughts on what we now call infinitesimals in his De Circuli Quadratura (On Squaring the Circle) helped Kepler out when trying to calculate the area of a circle, by picturing it as an infinite series of triangles. Cusa's reasoning for this was that the circle encompassed all other forms. Cusa's and Kepler's work was later important to Leibniz' Law of Continuity.
Tomorrow: his views on bringing religions together.