Roger Bacon, aka The Wonderful Doctor ; 1214-1294
Scholastic Theologian, and with Albertus Magnus one of the founders of the Scientific Method.
'There are two modes of knowing -- by argument and by experience: argument concludes and makes us grant the conclusion, but does not produce certainty and remove doubt, and enable the mind to rest in sight of the truth, unless it find it by the way of experience.'
Alleged to have invented gunpowder ; certainly experimented in optics, alchemy, geography and geometry.
Rickaby's "Scholasticism" has a section on him here http://www.nd.edu/Departments/Maritain/etext/scholas3.htm
The ORB Medieval Sourcebook has his 1268 On Experimental Science here http://www.fordham.edu/halsall/source/bacon2.html